>> the evidence at the scene makes us believe that something entirely different happened. >> he told me she fell 20 feet. where were the injuries? why did i not see what i expected to see? >> a search for the truth in the woods and water. >> if your theory is right, that is almost like she was being hunted. >> like a hare and a wolf. >> two chilling accounts of what happened to the mom they all adored. one seemingly unsolvable mystery. >> either you believe crazy story a or you believe crazy story b. both stories are crazy. which one do you want to go with? winding down a mountain in southwest colorado, waterfalls spill over granite and sunlight filters through aspens and evergreens. cottonwood creek -- an only-in-the-west sort of backdrop. these snapshots barely capture it, but who can resist trying? what a spot to preserve a memory. careful, though. this is wilderness. the dangerous kind. >> she's in the river. she fell and they can't find her. he thinks she's dead. >> reporter: the frigid currents here can take a life and also, maybe, sweep away secrets. >> it was the perfect place to commit a murder where nobody would see you. >> if you go into it looking for trouble, you're going to find it. >> reporter: and up in those mountains, sometimes questions are left behind. >> i don't have an explanation for this. but certainly it does truly haunt me. >> reporter: the story begins with those pictures. together they form a couple, husband and wife, leslie and fred mueller, married for almost 27 years. >> they were always super affectionate. they acted like they were two high school kids that had just started dating. they're just all over each other. >> and you're like, "ewww." [ laughter ] >> reporter: these are the muellers' three children -- amanda, the eldest, then ariel, and alex, the youngest and only boy. they were brought up in texas, near the town of san angelo, but for fun the family headed out to their second home in lake city, colorado. those photos of their parents were taken nearby. >> they both loved the cabin and going up to colorado. >> it was so pretty. it was in a valley, and there were just -- you would look and it would look like a postcard. mountains. >> there was a river running right near there. >> reporter: their rockies getaway was a family place to relax and escape their busy lives back home. what was life like up at the cabin? >> we would usually go in the summers. we would just go hiking together, horseback riding and just kind of hang out as a family. >> reporter: did you feel like there was a lot of family bonding? >> yes. >> reporter: going on at the cabin? >> yeah, definitely. we'd end up having a lot of fun with board games or going out hiking and doing all these different activities together. >> reporter: in texas, leslie had an ob/gyn practice and worked long hours delivering babies. and she was the area's first ob/gyn, female ob/gyn? >> she was. she was very much a pioneer in that sense. >> yeah. >> like, i think the more people told her you can't do this, she wanted to do it. >> uh-huh. >> yeah, she was very strong-willed and definitely a feminist in a way, that she was all about like i can do anything that any man can do and i can do it better. >> reporter: in 2004 leslie decided to make a change in her life. she retired from medicine and devoted her time to the church. she even studied theology. but most of all, leslie loved the outdoors, especially riding horses. >> i think if she had her choice, she would be riding horses every day and then practicing theology. and i'm sure she wished the days were longer. >> she's like superwoman. >> their mom embraced adventure, and she wanted her kids to as well. >> one time mom and i went, just the two of us. i hadn't been horseback riding in a while. and so i told her i didn't want to go more than maybe five, six miles. and she goes, "okay, well, i found this trail. it's eight miles, but you can do it." and by the time it ended, it was 16 miles. >> reporter: so she tricked you. >> yeah, but we had such a wonderful time. but the next day i was not moving. >> reporter: as for fred, he owned a multimillion-dollar company importing steel for construction. still, their dad wasn't all business all the time. >> in the traditional motherly roles, he would definitely step up and wasn't afraid to be mr. mom. >> reporter: the mueller kids say their parents fit one another perfectly. >> he'd make a point of every night to try to do something nice for her. >> he was so proud of her, too. >> they'd talk all the time. anytime that there was any type of disagreement about, you know, who -- the dishes weren't done or some "honey do" chore kind of a thing, they would talk about it until they were completely resolved. and then the next second they'd be all over each other again and be perfectly happy. >> reporter: it was a happy weekend at the muellers' colorado cabin. may 3rd, 2008. now that leslie was no longer working, she was spending much more time up here. that saturday the spring day was sunny, the high-altitude air still chilled. morning began with chores. >> i think we were unloading some hay, doing stuff kind of like that around the house. >> reporter: so was this just a very typical weekend in colorado? >> yeah. >> reporter: it was just alex, then 14, up with his parents on this trip. that afternoon, the three went to mass in town. later, after a snack, his parents suggested they cap off the day with a hike to photograph some stunning waterfalls nearby. >> i was pretty wiped out by that time, and i just kind of wanted to hang out in the cabin and just read a book or something like that. so i turned them down on going for the hike. >> reporter: fred and leslie headed off with her dog gracie, a border collie pup. >> i think she was only 6 months old. >> reporter: was she rambunctious? >> she was rambunctious, for sure. she's the type of dog that when the ceiling fan would be going, she would try to jump up and like follow it around. >> reporter: fred and leslie parked at the base of the trail. snow still covered the ground in patches. they hiked up, past a small series of waterfalls. up until they found the perfect spot for pictures. they had arrived at cottonwood creek. fred struck a pose first. next, leslie's turn. one more of fred, big smile. and then leslie again. this time with her beloved gracie. then something went wrong. >> it's like it's just happening in slow motion in front of me. >> reporter: in an instant, leslie was gone. >> at the waterfall, she's in the river. >> reporter: what happened at cottonwood creek? >> coming up -- >> is she dead? tell him it's too soon to know. >> the hunt for answers would start with a frantic search. >> at the waterfall she fell and they can't find her. >> it's his wife? >> yeah. >> where was leslie mueller, and did she survive? >> all of a sudden i hear yelling and the yelling is coming from downstream. >> when "dateline" continues. >> when "dateline" continues they help restore my natural barrier, so i can lock in moisture. we've got to have each other's backs... cerave. now the #1 dermatologist recommended skincare brand. save for being a new customer. save more for adding drivewise. save even more for driving safely. take another look at allstate -and start saving. visit allstate.com or contact your local agent today. alex mueller was alone at his family's vacation cabin in colorado. his sisters weren't on this weekend trip, and that saturday afternoon his parents went out for a hike without him. do you remember the last words you said to your mom as she was leaving the cabin? >> just "see you later," you know. >> reporter: just a normal, like of course i'm going to see my mom in an hour. >> yeah, exactly. i mean, nothing really memorable. >> reporter: and so then there's a whole period of time that they're gone. what's the next thing you remember? >> so reading, kind of hanging around. i think the first time i kind of noticed that it was getting a little late, it had gotten dark and, you know, nobody should be kind of hiking or walking around when it's dark. >> reporter: alex had no inkling of the tragedy unfolding at cottonwood creek. it started right after his dad took this picture of his mother, leslie. leslie and gracie posed here. you can see it's a stunning setting. but just about an arm's length behind me is a cliff. a steep drop-off to the granite below. and the icy cold waters of cottonwood creek. right after fred snapped the picture, leslie fell and was swept away in the water. unable to find her, fred raced for help, driving more than a mile to the nearest house. >> somebody just showed up at my house. >> reporter: with no cell service up by the creek, the owner of the house, justin sparks, was the first to call 911. >> he pulled up, he said, at the waterfall. she's in the river. she fell and they can't find her. he's frantic, of course. he said he thinks his wife's dead. >> it's his wife? >> yes. >> reporter: the homeowner offered right away to help fred. they sped back up the mountain, and fred dropped him off at a spot to begin searching. just down the road, physician's assistant and ems volunteer michael golub was on duty. >> a call went out over the radio for a female drowning victim. >> reporter: golob headed over to the base of the trail. there he ran into fred. >> he comes barreling down at a very high rate of speed and kind of slams on his brakes and starts yelling at me, "let's go. let's go. let's go." >> reporter: the ems responder noticed this man he was trying to help could also be injured. fred's face was scratched up. >> he has some superficial lacerations. and so i take a minute to make sure this isn't my second victim, to make sure he's okay. and he assures me he's fine, he's fine, just kind of wants to keep going. >> reporter: but then as fred drove, he seemed disoriented. he pulled over, but he couldn't seem to find where leslie fell. >> i start to unload from the jeep. he says, "no, this isn't it." and we get back in the jeep and he continues upstream or uphill. >> reporter: after another stop they found the right place and hiked toward the creek. >> all of the sudden i hear yelling and the yelling is coming from downstream. >> reporter: it was the homeowner justin sparks. michael golub took off toward him. he was in a knee-deep pool down below the waterfalls. >> there was mrs. mueller. she's dressed in a lime green jacket. and she's floating face up. he actually found her. i believe he used the word "pinned" under the log and face down. >> reporter: leslie had no pulse. but golub thought there was still hope that she could be revived. fred had caught up, towering over them from the creek embankment. >> he says, "is she dead?" i tell him it's too soon to know. >> reporter: golob sent fred back down the road to look for more help. by then, a small village of first responders had assembled at the start of the trail. among them was hinsdale county sheriff's deputy justin casey. >> we had other officers responding, but we also had the e.m.s. personnel coming in ambulances, and we had fire personnel coming with the fire trucks. >> reporter: dispatch put a call into then local sheriff ron bruce. >> we had gotten a report of a drowning up on cottonwood creek. and they said they'd keep me advised. >> reporter: by then a group of medical responders made their way up to the creek to help. but still, no heartbeat. not a breath from leslie. and it was clear she was gone. >> we were not going to be able to bring miss mueller back. >> reporter: at the cabin alex was wondering why his parents weren't back yet. their hike was only supposed to last an hour or so. but they'd been gone more than three hours. >> were you worried? >> not really worried as in something happened to them. just more like it's kind of weird that they would stay out past dark if they're going tore a hike. >> reporter: it was past 8:00 p.m. when his dad got home. without his mom. >> it's my dad and the deputy. and yeah, they come in. it's kind of a shock to see, you know, when you're expecting somebody, to see strangers coming in instead. >> reporter: what do you think when you see that? >> not a whole lot of time to think, honestly. you kind of go into shutdown mode. >> reporter: alex recalled his dad seemed like he was in shock. >> he was very disheveled, had been crying a lot. and then he, you know, gave me a big hug, and that was kind of how it broke. >> reporter: i can't even imagine getting that news, when you've just thought your parents were going for a quick hike. >> just kind of disbelief, really. the whole thing just seemed so surreal. >> reporter: then father and son were shuttled to the sheriff's department where fred could file a report about the accident. >> i remember them saying, "you take fred, i'll take alex." >> reporter: sheriff bruce was at the station to meet them. >> my initial reaction to fred was he was a victim, a grieving husband. >> reporter: fred gave a brief, handwritten statement. >> we want to make sure we've dotted the is and crossed the ts. we were dealing with the death of a woman. >> reporter: then fred and alex headed back to their empty cabin. and there, in that home that had until then been full of such happy memories, fred and alex endured the longest night of their lives. >> we stayed together in the same room the whole night. >> reporter: and did your dad sleep at all that night? >> it was a very long night. >> reporter: but they had no idea it was just the first sleepless night in what would become the longest ordeal of their lives. >> coming up -- >> we started taking photos. she took a few of me. i took some of her. >> fred gives investigators a detailed account of what happened to leslie. >> it looked to me like she just did a swan dive. and lands on the rocks right by the water. >> and he's very clear on who is to blame. >> it was that damn dog tangled up in her legs. is what i think it was. >> what would police think of that? when "dateline" continues. gmy c. what about rob's dry cough? works on that too, and lasts 12 hours. 12 hours?! who studies that long? mucinex dm relieves wet and dry coughs. i guess i look pretty... ridiculous. 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>> i don't even think i asked him what happened, because you don't want to hear details. i mean, i could easily say that was the worst day of my life, that i found out about my mom. and the only detail that matters, that she was gone. >> reporter: the tragic details, however, were the business of hinsdale county sheriff ron bruce. he and his small office have the huge job of patrolling more than 1,100 square miles of potentially dangerous wilderness and wildlife. should they have not gone -- >> oh no, no. >> reporter: -- to that area? or was it okay? >> it was perfectly fine. i think it -- he related it was something of an idyllic day. >> reporter: the day after leslie died, sheriff bruce stopped by the muellers' cabin to get a more precise account of what happened during that hike. bruce's undersheriff and a state investigator talked to fred. >> you know, i shouldn't have even taken her up there. it's all my fault. >> reporter: the conversation at the muellers' kitchen table was recorded. >> we started taking photos. she took a few of me. i took some of her. >> reporter: fred described in detail how that kodak moment went wrong. >> i suggested that she take a picture with her dog, and it's a border collie and it's a very -- it's just extremely skittish dog. she looks at me and i take her picture and we think everything's cool and i think like a bird kind of flutters by. >> reporter: fred said the rambunctious border collie got startled. >> but the dog just jumps out as she's turning and it's like -- it's like her feet just went out from under her. it's like it's just happening in slow motion in front of me. she falls forward and i remember lunging forward to try to get to her, but i was probably five, six, seven feet from her. >> reporter: fred said he witnessed leslie freefall. >> it looked to me like she just did a swan dive. and lands on the rocks, right by the water. just like head and shoulders and just crumples. and then just slides like mush into the little channel. and i'm screaming her name, i'm hollering. i should've just jumped in. >> reporter: fred said he lost sight of leslie in the water so he ran down to where he thought the current would take her. he said he got scratched up as he stumbled up and down this embankment, navigating rocks and running through bushes. >> i must have tripped, i don't know, a few times, quite a few times coming down. and i'm sure i obviously hit something coming down a few times. >> reporter: he told how he had left the camera with those last images of his wife behind. >> i would imagine i just dropped it while i was screaming. >> reporter: unable to locate leslie, he abandoned his search of the creek bed and made the decision to go for help. >> i hauled butt down to justin's house and i'm honking and i scream at him to -- you know, i think my wife's dead. >> reporter: after listening to fred's story, the sheriff wanted to go up to the site of the accident. you take fred back up to the mountain? >> yes, we did a walkthrough on the scene. >> reporter: up at the scene, fred repeated how the dog seemed to cause leslie's fall. >> it was that damn dog tangled up in her legs is what i think it was. >> reporter: gracie ran off into the woods right after the accident. a member of the sheriff's department later found her and took her back to his house. >> everything changed that day. >> reporter: changed forever in ways the kids could not, in their immediate grief, begin to grasp. that's because while their father was on that mountain talking to authorities, seeds of doubt were being planted right in the landscape around cottonwood creek. coming up -- one of those seeds found near the ledge where leslie spent her last moments. >> all at larm bells were going off. even to this day it gives me the chills. >> and a family worries about their grieving father. >> you just didn't know if he was going to do something crazy or if he was ever going to get over this and be able to move on. >> when "dateline" continues. hes there is a bit of a clogging problem. 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[screaming] [howling] laughter... and friendship. you accessorize with a sloth? this is belt! mine's sash. i'm milissa rehberger. here's what's happening. investigators have identified 63-year-old anthony warner as the person responsible for the christmas morning explosion in downtown nashville. warner was present when the bomb went off and died in the blast. president trump has signed congress's $900 billion covid relief bill, averting a monday night government shutdown. but it appears trump's approval comes at a price. the white house says the senate will start an investigation into the president's claims of voter fraud. back to "dateline." fred mueller spent the day after his wife's death talking with investigators about the accident on cottonwood creek. the next day he and his son alex flew home to texas, ferried by a friend in a private plane. >> you never think you would -- it could happen to you. >> reporter: there, fred and alex were reunited with amanda and ariel, alex's older sisters. >> you hear horrible stories and you feel for these people. it was surreal that we were now that family and now, you know, just trying to get through it. >> reporter: so many came to pay their respects. but mourning took its toll. >> i would hold myself together in front of people who would visit and then i'd go in the other room to cry and break down. >> it's natural. >> kind of just saving face a little bit. >> leslie the horse lover was buried on the texas ranch where she grew up riding. >> when the blur was over and you finally had time to process what had happened, what did you think about your mom and your future? >> i was angry. i was really looking forward to being pregnant and calling my ob/gyn mom anytime i had any kind of little odd thing happen. >> it was like two weeks before my graduation. it was like a week before my prom. like all these big things that weren't the biggest things in the world. but it was just, like, things that your mom should be there for. and i mean seeing us grow up. it's -- >> reporter: the kids weren't just grieving their own loss. they felt their father's too. >> i had never seen him so sad or, you know, you just didn't know if he was going to do something crazy or, you know, if he was ever going to get over this and be able to move on. >> reporter: and up in colorado, sheriff bruce wasn't moving on either. he still had questions about the accident and fred's story. he'd sent deputy justin casey up to cottonwood creek to document the site. casey brought his brother with him. they snapped photos and shot video along the way. >> we started below where mrs. mueller's body was found and took photographs below as we progressed upstream. >> reporter: as the casey brothers moved up the creek, they noticed that the creek's flow didn't seem very strong. >> it didn't push us around as we were walking. we were careful with our footing in the sense that there are slippery rocks underneath the water. but it wasn't hard to go against the current. >> reporter: the deputy couldn't help but wonder -- how had leslie's body floated so far? >> the water is coming down. but it's not a raging river. it's not fast moving. >> reporter: deputy casey reported back to sheriff bruce who by that time had talked to the couple who lived by the trail and had helped fred in those first, frantic moments. what they said cast a new light on fred's story of that awful day. >> little tickling at the back of their neck had sent up some red flags to them. >> reporter: they told sheriff bruce that as they called 911 and set out to help in the search, fred was frantic one minute, then seemed calm the next. >> they said the vibes were all wrong from him. they became very uncomfortable. >> reporter: did they kind of, like, in hindsight think back? or was it right then? >> they were immediately concerned that something was amiss. >> reporter: it was the husband, justin, who found leslie's body in the creek, but he told the sheriff that initially fred had sent him off to search too far downstream. >> he drove up a short ways and said he was sure that his wife's body was somewhere in that area. justin thought that was odd. >> reporter: was it possible that fred was disoriented? it's kind of a tough area to navigate. >> it's possible. >> reporter: yet sheriff bruce said he too got a strange vibe from fred the night leslie died, and again the next day, when they went back up to cottonwood creek. >> his emotions and his responses to everything seemed to be extremely flat. and i thought almost rehearsed. >> reporter: is that fair, though? with everyone being different in this world and everyone reacting differently to tragedy, is it fair for you to judge him based on how you think he should be acting? >> i don't know if it's fair. but in my business it's realistic. because you have to look at all angles of an event and make sure that you're uncovering everything that's there. >> reporter: on a ledge near where fred said leslie fell, investigators found fred's camera and the photos of leslie's last moments alive. as he stared at leslie, the vibrant wife and mother, sheriff bruce's gut told him keep looking. >> the vibes were all wrong. all the alarm bells were going off. even to this day, it a little bit gives me the chills. >> coming up -- vibes are one thing. but investigators thought they also had evidence that fred wasn't telling the truth. >> he told me she fell 20 feet. where was the trauma? where were the injuries? why did i not see what i expected to see? >> there were no broken bones. any substantial abrasions or contusions. >> what really happened to leslie that day? when "dateline" continues. honey honey? new nyquil severe honey is maximum strength cold and flu medicine with soothing honey-licious taste. nyquil honey. the nighttime, sniffling, sneezing, coughing, aching, stuffy head, fever best sleep with a cold medicine. every minute. understanding how to talk to your doctor about treatment options is key. today, we are redefining how we do things. we find new ways of speaking, so you're never out of touch. it's seeing someone's face that comforts us, no matter where. when those around us know us, they can show us just how much they care. the first steps of checking in, the smallest moments can end up being everything. there's resources that can inform us, and that spark can make a difference. when we use it to improve things, then that change can last within us. when we understand what's possible, we won't settle for less. the best thing we can be is striving to be at our best. managing heart failure starts now with understanding. call today or go online to understandheartfailure.com for a free heart failure handbook. to your friends... your family... to your teachers. in that spirit of giving, chevy's proud to give our employee discount to everyone. the chevy price you pay, ...is what we pay. not a cent more. because giving, ...and giving back, is what the holidays are all about. use the chevy employee discount for everyone to get a total value of over eight thousand four hundred dollars on this silverado. get the chevy employee discount for everyone today. >> reporter: for the folks charged with keeping the woods and waters around cottonwood creek safe, leslie mueller's drowning was a tragedy, but also a mystery. >> you know, i put myself in fred's shoes, and they didn't fit. >> reporter: sheriff ron bruce had thought fred's demeanor the day leslie died was unusual. fred, to him, showed a lack of emotion. but what really spoke volumes to the sheriff and his team was something they knew well -- the terrain around cottonwood creek. as fred told them, leslie did a swan dive from up there, landing on her head and shoulders on this rock. then she slid into the water. a horrible accident. but to local law enforcement, something seemed off. the first trained rescuer on the scene noticed it first. what appeared to be a major inconsistency in that story. after such a treacherous fall, leslie's body, when pulled from the creek, didn't look at all injured. >> he told me she fell 20 feet. where was the trauma? where were the injuries? why did i not see what i expected to see? >> reporter: one look at that drop off, and sheriff bruce was wondering the same thing. and when the autopsy report came back, it only heightened his suspicions. >> there were no broken bones, any substantial abrasions or contusions. they simply weren't there. >> reporter: every accident is different. every fall is different. is it possible that she just fell in a certain way that just didn't produce those injuries you were looking for? >> no. if she landed head first, as he told us she landed, she would have had head injuries, facial fractures, spinal trauma. none of that was present. >> reporter: so sheriff bruce made a quick conclusion. to him, no injuries meant no fall. fred had to be lying. >> what you see here, andrea, this is -- >> reporter: we went back to cottonwood creek with the sheriff in may 2014. that's the same month leslie died. >> we got a late snowstorm this year. >> reporter: a spring storm had just blanketed the woods and rocks. i have to say, i'm honestly nervous just standing here. >> it's -- >> reporter: this is very steep. >> that's a sheer drop-off. >> reporter: it was up here where they had posed for pictures that sheriff bruce showed me what he thought were key pieces to their puzzle. >> the evidence here at the scene makes us believe that something entirely different happened. >> reporter: they found trampled bushes, what they thought looked like scuff marks, and a pair of broken glasses that turned out to be fred's. >> there was evidence of a struggle in there. and that's where fred's mangled glasses were found. >> reporter: sheriff bruce formed a theory that after snapping those photos, fred and leslie got into a physical fight. >> we think that at that point, i think anyway, that she was able to break free of his grasp at that point. and she ran back this way and down, paralleling this path that goes down, eventually meets up with this stream. >> reporter: you think he chased after her? >> i think he paralleled her down that road till he got to the point where he could easily intercept her as she's going down by the stream. >> reporter: if your theory is right, that is almost like she was being hunted. >> it's almost like a hare and a wolf. >> reporter: and according to bruce's theory, fred chased his wife right into the shallow pool where she was found. >> that's where he held her underwater and drowned her. and then placed her right by the submerged log. >> reporter: but bruce admits investigators lacked some evidence to back up that scenario. what about footprints? there were no footprints in the mud or -- >> no. and by that time, we'd had investigators in here, and it'd been tracked up pretty good. >> reporter: so the evidence was ruined essentially. >> yeah. >> reporter: if there was evidence? >> right. >> reporter: the sheriff and agents from the colorado bureau of investigation, the cbi, worked together, investigating what they now thought was a homicide. they went down to where the muellers lived in wall, texas, to poke around in fred's life, but they couldn't find anyone to say anything bad about him. >> we found that the interviews were largely unproductive. >> reporter: so you were hitting walls? in wall, texas, which is an outlying community outside of san angelo. it's a pretty closed community. >> reporter: and inside that community none of leslie's friends or family doubted fred and couldn't understand why folks up in colorado were asking questions. >> yeah, people loved dad. that's why he had immense amount of support. >> reporter: and then, ten months after leslie's death, fred mueller got an invitation from the cbi. an agent wanted fred to come back up to colorado for a talk. >> he casually mentioned, like, "oh yeah, i'm going back to colorado. they wanted me back up there." he's just saying, like, "you know, i don't know what they're doing, either. but it's just -- we got to cooperate. they're doing their job. let's just get past it so we can move on." >> i just wanted to first, fred, thank you for coming. >> you're welcome. >> reporter: again he shared his recollections about that day at the vacation home. >> it was a beautiful day and it went to hell. there are so many things i wish i had done differently. >> reporter: and again described what happened to leslie after she posed for that last photo. >> she was flailing in the air, screaming. and i was screaming. and she hit and never made another peep. >> reporter: if fred's account of the accident was the same, the tone of this interview was different. the cbi agent made it clear they didn't believe his story. >> and, you know, i want to take this opportunity to ask you everything that's making me think that this may not have been an accident. >> ask me anything you want. >> reporter: they questioned fred about those broken glasses found at the scene. >> i'm just going to say it. i'm thinking you two had an argument by this bush. >> no, ma'am. no, ma'am. my wife and i did not have an argument anywhere that day. >> because you -- >> that was the best day of our lives until that accident. >> reporter: the best day of their lives? the agent clearly suspected there had been trouble in the muellers' marriage. a suggestion fred coolly dismissed. >> i can see after 27 years the two of you grow apart. >> no. i think we made a hell of a good pair. >> and you don't know quite how to deal with that. >> or. or. >> or? >> one could say that after the 27 years we were looking forward to retirement. >> reporter: and fred insisted that on the day she died he found her more attractive than ever. >> she was beautiful, and she knew that. and i would tell her that. she became more beautiful from being already beautiful in my eyes, became more beautiful as she became older. and we had a very -- that's probably none of your business. we had a very active sex life and we got along great. and if y'all did a good autopsy you would know that. you would know that. >> what are you trying to tell me? >> that we made love that morning. >> reporter: but even as the seemingly confident fred grew clearly irritated, the agent wasn't deterred. what about those scratches on his face the day leslie died? >> so these vertical scratches you're saying you got from bushes? >> bushes or that ground or running down this hill. falling a few times, which i did fall, but it had to have been from some of that. there's no other explanation. >> okay, well then -- >> that's factual. >> there was no altercation up there? >> no, ma'am. no, ma'am. >> because it looks -- >> check underneath her fingernails if you think there's something underneath her nails that's missing off my face. it didn't happen. there was no altercation. write it down. none. >> reporter: for now it seemed that was all the agents could do, document fred's story and let him leave. >> i'm sorry to be a crude open book. >> time is 11:23. i am turning off the recording. >> reporter: investigators had their theories, but did they have a case? fred went home to texas, where his family thought would be the end of it. >> his entire philosophy through all of this was it was an accident, i'm telling the truth. >> and he wanted to cooperate. he wanted to help them see that. >> reporter: but investigators hadn't seen that. not at all. and if fred couldn't answer their questions, they'd head back to cottonwood creek and hope that the water could. >> coming up -- fred has always said that water carried leslie away, to here, where her body was found. now investigators put that story to the test. >> we had to go back and try to duplicate the water flow as it was on the evening of the event. they said there was no way that her body could have ended up under that log unless it had been placed there. >> when "dateline" continues. that your digestive system isn't working at its best. taking metamucil everyday can help. metamucil psyllium fiber gels to trap and remove the waste that weighs you down. it also helps lower cholesterol and slow sugar absorption to promote healthy blood sugar levels. so you can feel lighter and more energetic. metamucil. support your daily digestive health. try new metamucil fiber gummies made with a prebiotic plant - based fiber blend that helps promote digestive health. thisgarnier createscream it's thenew serum creameam the power of a serum, the moisture of a cream, and the protection of an spf 30 3 products in 1 bottle, 1 step choose vitamin c or hyaluronic acid formulas that are clean and vegan for glowing, healthier-looking skin in just 1 step new garnier green labs serum cream by garnier, naturally! my job is to help new homeowners who have turned into their parents. i'm having a big lunch and then just a snack for dinner. so we're using a speakerphone in the store. is that a good idea? one of the ways i do that is to get them out of the home. -no. is that a good idea? we all see it. we all see it. he has blue hair. -okay. -blue. progressive can't protect you from becoming your parents, but we can protect your home and auto when you bundle with us. -keep it coming. -you don't know him. time went by and the muellers didn't hear anything from the colorado investigators. the kids assumed the sheriff and his team had finally decided to believe their dad too. >> we didn't hear from them for three years after that. and so i thought that -- >> i just thought it was done. >> yeah, we didn't -- >> i guess they finished up their -- >> crossed their -- >> -- paperwork or whatever they needed to do. >> -- "t"s and -- >> and that it was over. >> reporter: it wasn't over. >> i am an open book. >> reporter: in fact, after fred's interview with the cbi, investigators kept working. what drove them was their theory about a possible struggle, and that curious lack of injuries on leslie's body. but the sheriff knew they needed more, and he put that last photo of leslie behind his desk. >> she was my constant reminder. and that photo was what -- what was the nudge that kept me going on this case. >> reporter: investigators decided to zero in on one aspect of fred's story. was it really possible for leslie's body to float from where he said she fell to where she was found, 150 feet and three waterfalls downstream? >> when we brought in the really top-notch water flow experts, we had to go back and try to duplicate the water flow as it was on the evening of the event. >> reporter: in august 2009, 15 months after leslie died, investigators headed up to cottonwood creek to conduct some tests. they dressed a woman around leslie's size in similar clothing to what she wore the day she died. and positioned the female stand-in on the rock ledge, where fred said leslie landed before sliding into the water. >> the forensic people tried to float her from that location, where he alleged that she fell. the water did barely -- barely touched her body. >> reporter: so investigators put her in the water to see what would happen. >> she was then moved into the very center of that stream and it wouldn't budge her. >> reporter: finally, they went down to the pool where leslie was found. >> they then put her in a wetsuit, which gives her buoyancy. >> reporter: she was able to float. but unassisted, she had a hard time making it all the way to the log where leslie's body had been pinned. this meant something big to the investigators. >> so it belied what he told us about this raging torrent tearing her away from his view. >> reporter: they tried it all again with a mannequin, and again, what they saw did not match what fred recalled. in the deeper pools, the mannequin sank and it got stuck at the falls. >> each time she had to be physically moved over the lip of those waterfalls, the water, the stream would not move her. >> reporter: did you feel like because this case was hard enough as it was, that this testing had to be just as perfect as it could be? >> of course. with no witnesses, we're dealing strictly with circumstantial evidence. and circumstantial evidence is often enough to get you a conviction. but we knew we needed to have a lot of it. >> reporter: to investigators these tests confirmed their suspicions. to them, fred's story of leslie's accident was impossible. >> they said there was no way that her body could have ended up under that log, unless it had been placed there. that the forces of nature would not have put her under there. >> reporter: but were these tests enough to make a full-fledged criminal case? the first person they'd have to convince was the local district attorney. >> he was quickly brought on board as to what we were investigating and what our thoughts were. >> reporter: it turned out to be a hard sell. >> for whatever reason, we could never pique his interest. he never said no, but he just -- i didn't find the enthusiasm. >> reporter: even after those tests, the d.a. wasn't ready to press charges. months went by, then a year. leslie's picture was still there right behind sheriff bruce's desk, but the investigators weren't about to shelve their case. are there things happening? are the wheels turning? >> it was constantly on our radar screen, that there were things yet to be done. but the months did run on. >> reporter: all this time, fred was a free man in texas. >> his business ventures were moving on. and at home, we were all saying, "fred mueller believes he got away with murder." >> reporter: but sheriff bruce says fred mueller may have underestimated the hinsdale county sheriff's department. >> i think that was he -- what he thought. he was going to get some kind of bumbling buffoon to show up. and he was going to walk away on this. >> reporter: what do you say to someone who says, "you're a small-town sheriff who got tunnel vision, who focused on this rich outsider and just like a dog with a bone would not let go?" >> well, i'd say they're wrong. and i've got thick skin. we did the right thing. >> reporter: they kept working and testing and poking around, not sure if it would ever amount to anything. as the years moved on, investigators were continuing to build a case against fred. though his children were unaware their father was under such intense suspicion. they were trying hard to remember the happy moments with their mother and put the colorado tragedy behind them. what became of the cabin that held so many memories for all of you? >> i think after the accident it wasn't going to be a happy place for us anymore. and so dad decided to sell the place shortly after mom died. >> reporter: i would imagine that whole area's just kind of bittersweet now. >> unfortunately. it's a beautiful area. it's just -- >> not for us. >> reporter: for the mueller children, life seemed to be stabilizing. mandy was settling in with her husband. ariel was in college. and alex, a high school student, was dreaming of a career in the navy. but as alex said, his dad was having a harder time of it. >> he married mom when he was 18 or 19. he depended so much on my mother, and then to all of a sudden be kind of just cast adrift -- >> reporter: eventually, fred's counselors and friends suggested he was ready to meet someone new. >> he finally started getting back on his feet and started thinking about moving on, and he met wendee. >> reporter: wendee and fred were introduced through old family friends. >> she came into a very tough situation. but she also, she brought my dad out of a very dark place. you know, she saved his life, essentially, because he was so depressed. >> reporter: after two years as a widower, fred married wendee. >> she was really great and understanding and helped him move forward. >> reporter: a fresh start, such a long way from fred's tough grilling in colorado. he had good reason to think it was all over. >> there were times where we were real frustrated. when they say the wheels of justice turn slow, we felt like they were turning too slow this time. >> reporter: all the while, as the years are passing, you're looking at leslie's photo in your office every day. >> yes, i am. >> reporter: is that keeping you going, focused? >> absolutely. >> reporter: then, in 2011, two and a half years after leslie's death, a new d.a. took office, and the sheriff lobbied him to take action. >> we were able to get 30 minutes of his time and say here's what we're looking at, here's what we think occurred. he said, let's go. >> reporter: the d.a. assembled a team to look into the case. matthew durkin, a deputy colorado state attorney general, came on board. he was later joined by ryan brackley, on loan from the boulder county d.a. what was your first impression? >> very tough case. >> reporter: they combed though the case file -- fred's statements, leslie's autopsy, and all those tests conducted at the creek. >> this location was a breathtakingly beautiful place in the middle of nowhere. it was the perfect place to commit a murder where nobody would see you. >> coming up -- authorities take a close look at the scene. >> the defendant's story did not match up. >> and for the mueller kids a shock. >> i was just like, why? and they said, oh, well, we can't tell you that. >> a new chapter opens. but nothing in this case will go the way anyone thinks. when "dateline" continues. 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"your father's been arrested." >> reporter: did you say anything back to them when they told you? >> i was like why? and they said oh, well, we can't tell you that. we just have some great proof. and i said, well, it took you four years. what exactly are you doing? they said we just can't tell you that. >> did you ever think for one second, well there, must be something, he must have done something for -- >> no. >> -- him to be arrested, to be going through this? >> we never doubted his story. we never doubted. we never thought he would have done anything wrong or anything to hurt mom ever. that's something that i can't even fathom because he would have never done anything like that. >> the kids believed the authorities had it in for their dad and trumped up things that weren't true, like that their father showed no emotion after their mother's death. >> he was obviously panicked. he was panicking. he was shaking. he had been crying profusely. >> reporter: remember, only alex was in colorado at the time, and thinking back, he got angry about the way he and his dad were treated. >> they separate us, like you would with criminals. separate myself from my dad, put us in separate vehicles. >> reporter: to the kids, it all pointed to a rush to judgment that turned into an obsession. >> if you go into it looking for trouble, you're going to find it. >> we were also as a family never informed what they were doing at cottonwood creek, that they were paying for experts, doing all kinds of -- >> we didn't know what was going on. >> -- tests on the water and all these different things like that. but this was all like a closely guarded secret that they never felt they should share with either him or the family of the victim, of my mother. >> reporter: fred mueller spent the next year in jail in gunnison, colorado, awaiting trial. >> he sunk into such a deep depression right after mom died, and he kind of sank back into it while he was sitting in jail. >> and no one could get to him. it was more the fact that -- >> and we couldn't help. >> -- he was completely cut off -- >> isolated. >> -- from his family for a year. >> reporter: the kids were eager for their dad to take on his accusers. attorney roger sagal was part of fred's legal team. after reading through the discovery and the evidence, what were your first thoughts? >> why was this guy arrested for murder was my first thought. it was a question from the very beginning as to what evidence did they really have? >> reporter: he'd soon find out in court. more than four years after leslie drowned in cottonwood creek, fred mueller would stand trial for murder. >> coming up. the prosecution challenges fred's entire story including, stunningly, the one thing that never seemed in doubt. his rock solid marriage. >> fred was telling people that in fact the marriage had gone stale and that he did have a wandering eye. >> when "dateline" continues. ahoy! gotcha! nooooo noooooo quick, the quicker picker upper! bounty picks up messes quicker and is 2x more absorbent, so you can use less. bounty, the quicker picker upper. every minute. understanding how to talk to your doctor about treatment options is key. today, we are redefining how we do things. we find new ways of speaking, so you're never out of touch. it's seeing someone's face that comforts us, no matter where. when those around us know us, they can show us just how much they care. the first steps of checking in, the smallest moments can end up being everything. there's resources that can inform us, and that spark can make a difference. when we use it to improve things, then that change can last within us. when we understand what's possible, we won't settle for less. the best thing we can be is striving to be at our best. managing heart failure starts now with understanding. call today or go online to understandheartfailure.com for a free heart failure handbook. call today or go online to understandheartfailure.com robinwithout the commission fees. so, you can start investing today wherever you are - even hanging with your dog. so, what are you waiting for? download now and get your first stock on us. robinhood. >> reporter: 4 1/2 years after leslie mueller's death her husband friend's murder trial began in gunnison, colorado. their children and fred's new wife dropped everything to be in court and to pray that their dad would soon be cleared. are you all just anxious for this trial to start? >> yes, definitely. >> reporter: you're on pins and needles. >> i want to see why they put us through this. what do they think that they have? >> reporter: as the trial got underway that frigid january 2013, inside the courtroom the prosecution felt an icy chill. >> normally when you walk into a courtroom during a murder trial, it's very divided. i walked into that courtroom and everybody was on fred's side. leslie's family included. was that daunting to you at all? >> i wouldn't say daunting. it was certainly unique. but we had to stay focused on what we thought -- what we needed to do. we believed that the defendant was responsible for his wife's murder. >> reporter: it would all come down to two competing versions of what happened here. fred's story -- leslie accidentally went over this cliff and was swept away by the current. or the prosecution's -- that fred was lying to cover up leslie's murder. >> two people went on a hike, and only one person came back. >> reporter: the prosecution began its case with testimony about fred's behavior that day. they called jennifer sparks, whose house fred drove to looking for help. >> did you observe him become emotional at any time? >> no. >> reporter: she told the jury fred's lack of emotion concerned her. >> what conversation did you have with your husband at that time? >> i told him something's not right, be careful. >> reporter: her husband, justin, testified that fred's demeanor seemed staged as they drove together to look for leslie. >> it sounded like somebody was crying, but there were no -- there were no tears. he acted like he was very upset and then a few seconds later, he'd act like we were kind of buddies driving down the road in a car. >> reporter: the prosecution had hoped to bring the jury up to cottonwood creek. but in january the terrain was virtually impassible with snow and ice, so it was up to the prosecutors to set the scene and show why they thought fred's story defied common sense and science. >> injuries are going to tell you a story that leslie mueller was drowned by her husband. >> reporter: prosecutors called michael golob, the first trained rescuer on the scene. >> i'm asking him what happened, tell me how, what happened. and he relates that she apparently had fallen off a waterfall. >> reporter: fred told golob the same thing he'd told investigators. he'd watched leslie swan-dive off the cliff, hitting granite, before sliding into the water. >> all of a sudden i was struck with the fact that this didn't -- there was no trauma. >> did you see any blood on leslie mueller? >> there was no deformities. there was no blood. >> reporter: even leslie's clothing seemed unscathed. >> did you notice any markings, tears, scrapes on the jacket? on the coat? >> there was none. it was remarkably pristine. >> reporter: the pathologist who performed leslie's autopsy was also surprised by the lack of injuries to her body. >> did you observe any injuries to mrs. mueller that were consistent with breaking a fall? >> no, i did not. >> did you observe any consistent with falling on her head and shoulders off a cliff onto granite as described to you? >> no. >> reporter: and what's more, investigators found no forensic evidence that leslie ever hit that rock. >> there was no fibers on this rock. there was no blood on this rock. there was no hair on this rock. >> reporter: this is a very unique case in the sense that the evidence is lack of evidence. there's no evidence. >> that's the tough part of the case. what we have is a lot of evidence that what the defendant said is impossible. >> reporter: and here was the heart of the prosecution's case, those tests investigators conducted up at the creek, tests they said proved fred's story was a lie. they showed the jury the video of those tests, pointing out, in one, how the female stand-in wasn't swept downstream and in another the mannequin wasn't washed over the waterfall and eventually sank to the bottom. >> are you seeing any sliding of the mannequin into the water? >> no. >> any washing or oozing? >> no. >> reporter: the prosecution's drowning expert was blunt. to her, fred's story was pure fiction. >> the water, there's nothing in that environment water-wise that could have gotten her to that spot. a human being had to physically put a body in that position. >> reporter: so what really happened? in court, the prosecution could only hint at the dramatic story the sheriff told us. his theory of a struggle, a chase, and a drowning. well, there were no witnesses for any of that, so it never actually was presented as evidence. but an investigator who searched the area where fred said lesley fell did testify about finding fred's broken glasses. >> this side was broken. the left-hand side was sticking in the dirt. >> did you see anything on the ground? >> four foot from the glasses there were what appeared to be scuff marks, as if somebody had slipped and had moved the dirt. >> reporter: and on the stand this witness, the coroner -- >> those are the gloves that leslie was wearing. >> reporter: -- tried to connect those scratches on fred's face to the plastic bumps, or nubbins on leslie's gloves. >> to me those plastic nubbins are a lot more consistent with the scratch marks on mr. mueller's face than branches and twigs. >> reporter: however, after a defense objection, the judge ruled the coroner's statement conjecture and told the jury to disregard it. so even though the prosecutors were not allowed to tell the jury how they thought the murder happened, they still had a theory to present for the why. they were high school sweethearts. he had never abused her, to anyone's knowledge. he had no life insurance policy out on her that he was trying to collect. what is the motive? >> fred was telling people, one being an employee of his, another being a close friend, that in fact the marriage had grown stale. that it was the same old same old between he and leslie, and that he did have a wandering eye. >> reporter: and according to the prosecution, his eye had wandered here. >> we were very good friends. >> reporter: jeannie barnes, fred's former assistant, testified that fred called and texted her a lot outside of work. >> did that ever make you uncomfortable? >> a little bit. >> reporter: and once fred talked to her about leslie and divorce. >> he had just kind of mentioned that their interests had kind of grown apart. >> reporter: so, according to the prosecution team, fred picked an idyllic spot in the middle of nowhere to find a way out of his marriage, and then concocted the story of her fall as a cover. >> two people went up, one came back. and we've only got his story. and we know that story is false, through and through. >> the defendant has asked people to believe what is impossible. impossible! >> reporter: but fred's lawyers were about to turn the state's case on its head. those tests at cottonwood creek, in fact any so-called "evidence of murder," just didn't hold water at all. coming up -- defense experts tell the jury that the way leslie died is absolutely clear. >> what was it in my opinion? accident. that's what i would have put on the death certificate. >> when "dateline" continues. ism it's the first serum cream garnier creates new serum cream the power of a serum, the moisture of a cream, and the protection of an spf 30 3 products in 1 bottle, 1 step choose vitamin c or hyaluronic acid formulas that are clean and vegan for glowing, healthier-looking skin in just 1 step new garnier green labs serum cream by garnier, naturally! [phone rings] "sore throat pain? try new vicks vapocool drops in honey lemon chill for a fast-acting rush of relief like you've never tasted in... ♪ honey lemon ahh woo vicks vapocool drops now in honey lemon chill that came from me. really. my first idea was "in one quarter of an hour, your savings will tower... over you. figuratively speaking." but that's not catchy, is it? that's not going to swim about in your brain. so i thought, what about... 15 minutes. 15 percent. serendipity. 15 minutes could save you 15% or more on car insurance. i'm milissa rehberger. here's what's happening. president trump has signed congress's $900 billion covid relief bill, averting a monday night government shutdown. this decision comes less than a week after the president demanded changes suggesting he would refuse to sign it into law if they were not met. and investigators have identified the person responsible for the christmas morning explosion in downtown nashville. the u.s. attorney confirmed 63-year-old anthony warner was present when the bomb went off and died in the explosion. back to "dateline." >> reporter: for three cold colorado weeks, as prosecutors laid out their case for murder, fred mueller's defense attorney roger sagal sat by his side. how was fred feeling throughout the trial? >> he was nervous. his life was on the line. it was tense. there's no doubt about it. it was stressful. >> reporter: fred's children found it especially hard. >> it was the worst experience you can imagine. the worst day of your life, imagine that being analyzed by a roomful of people and drug out publicly and scrutinized. your personal, private tragedy being exposed to the world and picked apart. >> reporter: to the siblings, each day in court felt like an unrelenting attack against their family and their father. >> you can't react. >> you can't say anything. >> you just have to sit there and take it and watch them say all these horrible accusations about my dad. >> you're looking for one person to stand up and say, like, this is preposterous. this entire -- there is no evidence. he's a good guy. he's never shown any history of violence. and, you know, and it was his wife, for goodness sake, and can we just -- we're stopping this. >> reporter: now fred's lawyers were ready to push back. defense co-counsel mike deguerrin told the jurors there was an obvious rush to judgment that contaminated the entire investigation. >> kind of an evil suspicion from the get-go. >> reporter: first-responder michael golob testified that neighbor justin sparks started making accusatory comments while they were still trying to revive leslie. >> justin at one point turned to me and said something along the lines of "i never trusted that s.o.b." >> i think that the suspicions started with mr. sparks and never stopped. >> reporter: you think it was somewhat of a snowball effect. >> yeah, i do. >> reporter: and even though golub was a prosecution witness, he admitted he personally didn't find anything odd about fred's behavior that day. >> he just kind of seemed to have trouble focusing, he seemed panicked. everyone deals with tragedy different. i felt in the context it seemed appropriate. >> reporter: but what about that important evidence against fred, the apparent lack of injuries on leslie's body? did you wonder at all why your mom didn't have more injuries, as some people feel she should? >> i don't. no. >> no, you can't say what people are supposed to -- >> she was bundled up. she was in cold water. we've thought about this more than anyone should ever think about what their body -- mother's body did after she died. >> reporter: the defense called its own forensic expert -- veteran pathologist werner spitz. he testified there were some injuries. bruising on her hand, and an apparent small skull fracture that no one else had highlighted. >> if you look carefully at this, you will see that there is an area here that is not like it should be. >> reporter: after looking at the medical examiner's report and leslie's x-rays, dr. spitz said there was no evidence this was a homicide. >> what was it in my opinion? accident. that's what i would have put on the death certificate. >> reporter: a veteran emergency room doctor backed up spitz's conclusion, saying not all falls are catastrophic. >> i don't see how you could rule out a fall from any of the circumstances or injuries that i've seen. >> reporter: and then it was time to counter all those prosecution water tests, the backbone of the state's case. the defense saw major problems with those tests and called its own water expert, a hydrologist who'd been measuring current flows for 40 years. >> increase of stream flow and as a general rule that increase comes in the late afternoon and evening. >> reporter: the defense expert pointed out that water in the mountains changes constantly, and in 2008, the year leslie died, there was more snow melt than usual. >> was 2008 a high-water year? >> it was a tremendously high-water year. >> reporter: those prosecution tests were done more than a year later, and in a different season, not spring but summer, when the creek's water level is usually lower. >> the flows on august 4th and 5th, '09, were less than the stream flows on may 3rd and may 4th, '08. >> reporter: all that so-called evidence that proved fred's story was impossible? the defense said it was useless. >> the testing that you do in 2009 is not necessarily going to be reflective of what did or did not happen in 2008. the bottoms of the creek changes, the walls of the creek can change, there's erosion upcreek, and you can see it the more times you go up there. you can see, every time it seemed a little bit different. >> reporter: and the defense attacked the state's expert for what it said was another flaw with the mannequin test. >> you did not start that test with the mannequin falling from the ledge, right? >> absolutely not. >> and therefore your testing did not account for any kinetic energy that would have been initiated from the fall, correct? >> that's correct. >> reporter: and what about fred's story? a jumpy dog distracted by a blue jay and a swan dive toward the rocky water? the defense said it was the truth, and not at all far-fetched. >> it is steep and angular and there's ice on the rocks. it's slippery. so it seemed perfectly plausible that she had fallen and floated. >> reporter: the defense brought in a canine behavior expert who analyzed that last photo of leslie and said the young border collie looked spooked and ready to bolt. >> the dog is under stress. the dog is pushing back. he's pushing back from mrs. mueller. she's trying to control him with the ear pinch and the dog is looking totally off in another direction. >> reporter: to the defense, it was clear. fred's story was entirely plausible, and the prosecution's was not. >> why would he do this? why would a guy who was married 27 years with no history of violence, no history of any sort of domestic disputes, all of a sudden decide on his vacation that he was going to murder his wife with his bare hands? i mean it just seems, that part of the case seems so farfetched. >> reporter: friend after friend arrived from texas to support fred. even his in-laws took the stand. leslie's own mother, ginnie, vouched for her former son-in-law's character. >> all those years any signs of fred being abusive or violent to leslie? >> no, i never saw a sign of fred being violent to anyone. >> reporter: and each of fred's children also faced the jury to tell them about their parents' long and happy marriage. ariel described one nightly routine. >> mom and dad would walk to the pond that was in front of our house about 200 yards, holding hands, and they'd be out there 30 minutes or an hour while the sun would be setting. >> reporter: amanda recalled how devastated her father was in the wake of her mother's death. >> i know he wasn't sleeping well. he would stay in bed a lot during the day. he cried all the time. >> reporter: and alex's testimony brought out an emotional response from fred in court. >> did you ever see your dad able to get over it? >> no. i'm looking at him right now and he's not over it. >> reporter: but what about fred's former assistant, the woman who'd given prosecutors a semblance of motive? in fact, during cross-examination, the assistant said fred and his wife showed affection for each other all the time. >> if he was at his desk, she would come in, she'd go straight to his desk, she'd give him a kiss and she would go back to her desk in the back. >> the absolute bottom line is there was no affair with jeannie barnes and fred did not kill his wife and he certainly did not kill his wife for jeannie barnes. >> reporter: the defense was sure it had shown the jury who fred really was. the people who knew him best said no way in the world could he have killed his wife. but now it was up to 12 people who didn't know fred at all to decide whether he did. coming up -- waiting for a verdict. >> the longer it took the more we were getting nervous. >> and then a bombshell. >> i was almost in tears. >> when "dateline" continues. dad! guess what i found! something under the porch? 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download now and get your first stock on us. robinhood. >> reporter: after a contentious five-week-long trial, the murder case against fred mueller finally went to the jury. what was it like waiting for that so important verdict? >> butterflies. >> yeah, we were all so nervous. >> and tension. >> but we were also -- i think we were all pretty confident in our gut that there's no way that he will not be, you know, acquitted. >> reporter: day one of deliberations came and went without a verdict. as the waiting spilled into day two, the defense and prosecution agreed on one thing. >> that is the toughest time of the trial, is the waiting. >> you're literally in this holding pattern. >> that's the worst part of any trial. just not knowing what the result was going to be. >> reporter: sheriff bruce was back in his lake city office, waiting by that photo of leslie. >> i had no concerns. we were going through the process. and then i'll admit a little, i questioned why it was taking so long. because i thought we had -- it wasn't a slam dunk, but i thought we had a solid case. >> reporter: at the courthouse, the jury was still out -- three days, no decision. >> the longer it took the more we were getting nervous. because it seems so clear-cut. >> it seemed obvious to us. >> reporter: it was the fourth day of deliberations when the jurors sent out a note. everyone gathered in the courtroom to hear what they had to say. >> we are at an impasse. >> reporter: the judge offered them lunch and asked for one more try. fred's future was in their hands. >> please rise for the jury. >> reporter: ten minutes later they'd passed on the free food and were back. >> ladies and gentlemen, i do have another note from you folks and it indicates that we are deadlocked. >> reporter: hopelessly so. the judge had no real choice. he declared a mistrial. >> it was extremely disappointing. >> very disappointing. >> extremely disappointing because it was not the answer that we thought we deserved, that we did deserve. >> mostly i felt for fred, you know, ultimately it's his life that's on trial, and so i felt sad for him that we couldn't get this resolved for him in the form of an acquittal. >> reporter: in fact, the defense had been very close. 11 of the 12 jurors voted not guilty. >> when i heard the jury vote, i was almost in tears, and i thought, how did they miss what we were trying to say? >> reporter: after the mistrial, the defense argued for his release on bond and the judge granted it. >> i just -- i can't wait to be able to give him a hug and just talk to him whenever i want. >> reporter: now, one full year after losing his freedom, fred was going to get out of jail. his daughters and new wife, wendee, gathered to embrace him. son alex, who was traveling, called in for an update. >> we're all at the jail right now just waiting for your dad. it's alex. >> we hadn't given him a hug in a year. we haven't been able to see him in person in a year. >> yay. >> i love you guys. >> it was so wonderful to get that hug that we had waited for. >> reporter: do you remember what you said to him? >> i love you. i love you. >> let's go home. when's the next flight out? >> come on, let's go home. >> it was so emotional. we were all so excited. we finally got to take dad home. >> reporter: home to texas, but for how long? fred was only out on bond. he still was charged with murder and had the threat of a retrial hanging over his head. >> we were extremely hopeful that they could change their minds and decide not to go forward again. >> and we were really hoping for that. >> reporter: more than just hoping. in fact, the family actually met with prosecutors and lobbied against another trial. did that weigh into whether to go to a second trial at all, the fact that this entire family, leslie's family included, did not want a trial? >> absolutely. we have to consider their position. we have to consider where they're coming from. >> reporter: then one part of the decision was made for them. the judge threw out the most serious charge, first-degree murder. why? the judge ruled prosecutors didn't have enough evidence to establish premeditation. >> we did manage to get an acquittal on the first-degree murder charge. >> reporter: prosecutors could still move ahead with second-degree murder, but would they? that 11 to 1 vote surely made a retrial daunting. >> 11 to 1 is not a great outcome for the prosecution's perspective. >> reporter: but the prosecutors spoke to some of those jurors and found out to many of them not guilty didn't mean innocent. >> and kind of behind those numbers were a group of people who by and large felt that something had happened here, that fred mueller was not telling the truth. >> reporter: prosecutors weighed it all and made their decision. fred would stand trial for murder again. >> i remember having a moment thinking, i can't do this again. and my mom always would be like, well, you're going to do it. and i felt like she was like, you're going to be fine and it's going to be good. >> reporter: your mom was kind of guiding you through in your head. >> yeah. she was always kind of, "suck it up. you can do it." >> reporter: but the second trial would by no means be a carbon copy of the first. with new attorneys and new witnesses, both sides hoped that this time they'd see a different result. coming up -- the defense comes out swinging. >> what the prosecution asks you to believe is that fred mueller went from this to a homicidal maniac within seconds. >> but then a defense witness says something that might do fred more harm than good. >> fred is very successful. he could sell anything. >> would jurors think fred had sold everyone a lie about what happened to leslie? 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>> i did feel that way. we could cut out the extraneous stuff and really focus on the case. >> reporter: but there were differences from the first trial. to ensure an untainted jury pool, the case had been moved northeast to suburban denver, more than 250 miles away from cottonwood creek. >> the evidence in this case is that leslie mueller did not fall off a cliff. >> reporter: this time from the prosecution, jurors heard a streamlined version of events and how, according to the state, fred mueller told a story that defied logic. >> like most murders, this one is hard to explain, doesn't make sense, doesn't make sense how and why this could happen. >> reporter: the witnesses to that awful day again came forward. neighbor jennifer sparks again told how she thought fred was acting strangely when he pulled up to her house. and she added this new detail -- >> he was petting my dog. >> and he was squatted down petting that dog? >> yeah, the dog was right here and he was just petting the dog. >> she felt that the defendant's demeanor was oddly calm. and that he bent down and petted the dog. she felt like his demeanor was misplaced. >> reporter: for the prosecution, this trial was a second chance to explain to the jury how fred's story didn't match up with the landscape. >> this area was not vast. it wasn't huge. it was actually quite tight and it was actually quite small. and making the defendant's statement impossible. our primary goal in the second trial was to get that jury to the scene. >> reporter: the judge considered a visit to cottonwood creek but ruled it was too expensive and impractical to bring the jury that far. >> not being able to do that, we did our best in the second trial to bring the scene to the jury. >> reporter: this second jury had a new 3-d model of cottonwood creek to examine and fresh testimony to consider. that apparent small skull fracture of leslie's that the defense highlighted in the first trial? no way, said the state's new witness, who was an expert in reading x-rays. >> could you determine that there was any evidence of a fall from 20 feet onto a hard granite surface? >> i didn't see any evidence of that kind of trauma. i didn't see any other fractures. >> reporter: prosecutors hammered home their key points -- leslie had no injuries from a fall and tests showed she could not have floated downstream, as fred said she did. >> it just doesn't seem as a likely scenario. >> reporter: so they argued fred must have drowned her right where she was found, right after a violent struggle. >> it was our intention to streamline the second trial as much as possible and focus in on the critical points of the case. >> reporter: but fred mueller also changed things up in this trial. he hired a new powerhouse attorney, pamela mackey, who had a roster of high-profile clients, like kobe bryant. >> what the prosecution asks you to believe is that fred mueller went from this to a homicidal maniac within seconds. >> reporter: fred's new lawyer argued that the state's case was beyond flimsy. >> their theory that because leslie mueller did not suffer any significant injuries in her fall from the ledge, fred mueller must have drowned her. that's their case. they won't give you the why of that theory. they won't give you the how. >> reporter: the defense again criticized the prosecution's recreations and told this jury there was no way anyone could know for sure what the water flow and depth were on the day leslie died. >> if someone measured the actual stream flow of cottonwood creek within days or a week of the incident it would have been informative. >> reporter: and several new defense witnesses took the stand. there was a biomechanical engineer who'd examined the mannequin used in this test. >> well, frankly, i mean, it's not even right to call it testing. >> reporter: according to the defense's new expert, the state's test had a big flaw. that dummy couldn't sink or float in water the same way a human does. in fact, it wasn't even designed for this sort of experiment. >> as far as buoyancy is concerned, it is not a scientific instrument for determining that, so it's the wrong tool for scientifically probing. >> reporter: and this time the defense brought in a memory expert to explain away possible holes in fred's story. the expert said extremely stressful situations can play tricks with memories. so maybe fred didn't actually see leslie fall on her head, as he said he did. >> false memories happen to us all the time. it's not a lie. it's just a memory that happens to be incorrect. >> reporter: but no expert could help the jurors understand how fred truly felt about his wife of almost 27 years. to wrap up their case, the defense brought up fred's family to talk about how happy the muellers had been. >> did you observe anything that led you to believe that your folks were having difficulty in their marriage? >> no, never. >> reporter: leslie's mother, ginnie, again defended fred. >> i've always had a good relationship with fred. >> reporter: but the prosecution's ears perked up when she offered a new detail about her son-in-law. >> yeah, fred is very successful. he could sell anything. he's a wonderful salesman. >> reporter: in final statements, the prosecutor used those words against fred. >> what we learned about the defendant yesterday is that he can sell anything. but he can't sell you the impossible. >> from our perspective, that's what he tried to do. is that he tried to sell the emergency responders, c.b.i., the sheriff's office and, quite frankly, these juries, tried to sell something -- a story that was just simply impossible. >> reporter: could this jury rise to the challenge and once and for all make sense of what happened at cottonwood creek? coming up -- jurors get the case. >> either you believe crazy story a, that she fell off that cliff and three waterfalls, or you believe crazy story b, that fred, who has no history of violence, killed his wife. both stories are crazy. which one do you want to go with? >> when "dateline" continues. e. understanding how to talk to your doctor about treatment options is key. today, we are redefining how we do things. we find new ways of speaking, so you're never out of touch. it's seeing someone's face that comforts us, no matter where. when those around us know us, they can show us just how much they care. the first steps of checking in, the smallest moments can end up being everything. there's resources that can inform us, and that spark can make a difference. when we use it to improve things, then that change can last within us. when we understand what's possible, we won't settle for less. the best thing we can be is striving to be at our best. managing heart failure starts now with understanding. call today or go online to understandheartfailure.com for a free heart failure handbook. call today or go online to understandheartfailure.com robinwithout the commission fees. so, you can start investing today wherever you are - even hanging with your dog. so, what are you waiting for? 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[ ding ] you got paid! that means adding people to the payroll. hi mom. that means... best burger ever. intuit quickbooks helps small businesses be more successful with payments, payroll, banking and live bookkeeping. see every yikes...... and even every awwwwwwww... wait, where was i? introducing self protection from xfinity. designed to put you in control. with real-time notifications and a week of uninterrupted recording. all powered by reliable, secure wifi from xfinity. gotta respect his determination. it's easy and affordable to get started. get self protection for $10 a month. >> reporter: it took more than five years, dozens of witnesses and hundreds of pieces of evidence in two colorado courtrooms to get to this moment. again, 12 men and women were trying to decide if leslie mueller was murdered or a victim of a freak accident. >> we all agreed that the accident, the fall, was completely crazy. and i just kept thinking, well, crazy things happen in life all the time. >> reporter: we spoke to 7 of the 12 jurors. >> either you believe crazy story a, that she fell off that cliff and down three waterfalls, or you believe crazy story b, that fred who has no history of violence killed his wife. both stories are crazy. which one do you want to go with? >> reporter: what were the key pieces of evidence for you or the lack thereof? >> lack of injuries. >> reporter: you felt that she should have had more injuries? >> absolutely. i mean, to fall 15 to 20 feet onto a granite platform. >> face first. >> and to go down head-first. down three waterfalls and be pulled out and be described as pristine? >> reporter: show of hands of who believed fred's story. >> we did take -- at one point in time we all said -- >> i kind of -- >> let's vote and see who thinks he's lying. and we all raised our hands. okay, we convicted him of lying. >> the question beyond that was my question is, if we don't believe his story, does that make him guilty? he is not on trial for lying. he's on trial for murder. and i need to know how and why. >> reporter: the jurors wondered where was the evidence that fred drowned her? if he really did kill her, prosecutors never provided any clear explanation of how he did it. >> there was no evidence to put him down at the recovery site. there were no footprints in the snow. and there was no defensive wounds on her. if there was a scuffle, i would think she would have -- >> she would have fought back. >> -- some bruises. she would have fought back. >> reporter: they pored over technical testimony about water in the creek. to them that flood of data and expert testimony was a complete wash. >> you can bring all the experts in and all the water tests, and it was just pointless because they'll always poke a hole in it because it wasn't done may 3rd, 2008. >> reporter: like the jury before them, this group's first day of deliberations ended without a verdict. >> as the deliberations took longer and longer, it became clear that we needed to be nervous again. >> reporter: while sheriff bruce felt more confident than ever this time around. >> i slept well. i ate well. i went about the rest of my normal duties at work here without a whole lot of concern about it and just expected that phone call to come in and say, "we got him." >> reporter: the 12 jurors returned the next morning, determined to make a fresh start. was anyone here consistently thinking about leslie, the mother, the wife, the doctor? >> we had little pictures up and everything. and i made the comment, like, "leslie, talk to me, say something." because she can't speak. >> right. she needed us. >> reporter: after two days of intense debate, the 12 jurors thought they were done. they sent out a note and the judge called everyone into the courtroom. >> ladies and gentlemen, you have sent me a final note indicating that you do not believe that you can reach a verdict. mr. foreperson, is that correct? >> that is correct, your honor. >> okay. i am going to declare the jury deadlocked in this case. >> reporter: hopelessly deadlocked, a second jury unable to say for sure if fred mueller had killed his wife or not. when you hear those two words again, "hung jury." >> it's crushing. >> absolutely crushing. >> reporter: disappointment again on both sides. do you ever look back and think, you know what? maybe we shouldn't have done this. it wasn't there from the beginning. >> absolutely not. >> no. >> both these trials were worthy of prosecution. a woman was murdered and both the efforts were more than worth it. >> reporter: so how close was the jury's vote this time? eight jurors believed fred was guilty and four voted to acquit. >> i have too many questions that are unanswered. therefore, i have reasonable doubt. >> we just couldn't come to agreement, you know. i was steadfast guilty and he was steadfast not guilty. and we tried to get everybody's impression of what happened or what they thought. >> reporter: the prosecutors wondered, could one decision by the judge have changed it all? >> to this day i believe that had either one of these juries been able to go to that scene, perhaps it would have been a different result. >> reporter: and then, three weeks after the second mistrial, an announcement. the state dropped all charges against fred mueller. >> when we finally got the news, it was like overwhelming with joy. we finally can rest at ease. and my dad can move on with his life. and we can finally just move on and -- >> relax. >> reporter: fred and his wife wendee have returned to texas, where fred still runs his thriving business. in colorado the case officially remains open. >> without any further investigation, without any further witnesses that could come forward to provide some new bit of evidence, at this point the case is -- just simply remains open. >> reporter: so fred will essentially have this hanging over his head potentially forever? >> at this point the case remains open. >> reporter: fred told us he's well aware of this legal limbo. he said he wanted to do an interview with "dateline" but is concerned that anything he says could be distorted by the prosecutors and investigators who still believe he did something wrong. >> leslie got to me. >> reporter: and that picture of leslie was prominently displayed in sheriff ron bruce's office. until he retired in early 2019. he says the photo is still with him. >> i think it was just the magnitude of the terrible tragedy that stuck with me and will stay with me the rest of my life. >> reporter: you get teary-eyed when you talk about this woman you've never even met. >> correct. >> reporter: who's not even a member of your family. >> yeah, i do. >> reporter: what is this connection you feel with her? >> i don't have an explanation for this. i can't put a finger on it. but certainly, it does truly haunt me, yeah. i feel like i let her down. >> reporter: leslie's family chooses to remember her vividly not as a victim, but as a cherished wife and mother they lost too soon. >> we don't want people to forget about how wonderful of a person she was before the accident and all the great things that she did. >> all the babies she delivered. >> lives she saved. just a great, great person. >> reporter: with the vacation home the muellers once loved long sold, they are making new memories as a family far from colorado. and in those magnificent rockies? seasons change, waters rise and fall, and some believe the secrets of cottonwood creek will remain a mystery forever. this sunday, what kind of president will joe biden be? >> faith in our institutions held, the integrity of our elections remains intact. >> we take a look at what joe biden has said through the years and on the campaign trail, on foreign policy. >> someone said to me in another interview, do you want to own afghanistan? i said, no, but we've got to rent it for a little while here. >> domestic policy. >> we've always moved forward as a nation when the middle class grows. when they grow, the poor have access and the wealthy get wealthier. >> and on governing a divided america. >> when we beat donald trump, you're going to see a great impediment taken out of the way. >> our look back and ahead at the man who's been running for decades. >> i announce my

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