details. that was the worst day of my life that i found out about my mom. >> a loving couple. a romantic hike. a secluded spot. >> she was turning to look at the bird. it's like her feet just went out from under her. >> all of a sudden i hear yelling coming from downstream. there was mrs. muller floating face up. >> a wife falling to her death. her husband falling apart. >> he was panicking and shaking. crying. >> the evidence at the scene makes you believe 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 truth in the woods and water. >> if your theory is right, it is. loo like she was being hunted. >> almost like a hare and a wolf. >> two chilling accounts of what happened to the mom they adored. one seemingly unsolve able mystery. >> you either believe crazy story a or 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 filtered through aspens and evergreens. cottonwood creek. an only in the west sort of backdrop. what a spot to preserve a memory. careful though, this is wilderness. the dangerous kind. >> she's in the river. >> reporter: the frigid currents can take a life and maybe sweep away secrets. >> where is the perfect place to commit a murder where nobody would see you? >> if you go into it looking for trouble, you will find it. >> reporter: and up in the mountains, sometimes questions are left behind. >> i don't have an explanation. but it haunts me. >> reporter: the story begins with those pictures. together, they form a couple. husband and wife. leslie and fred mueller. married almost 27 years. >> they were always super affectionate. they acted like two high school kids that had just started dating. all over each other. >> it was like ew. >> reporter: these are the mueller's three children. 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. you would look and it looked like a postcard. mountains. >> there was a river running right near there. >> reporter: their rockies get away was a family place to escape. >> what was it like? >> we would go there summers. hiking and horse back riding and hang out as a family. >> was there a lot of family bonding? >> definitely. we had a lot of fun. board games, going out hiking an doing all these different activities together. >> reporter: in texas, leslie had an obgyn practice and worked long hours delivering babies. >> she was the area's first female obgyn. >> she was. she was very much a pioneer in that sense. >> she was very strong willed. a feminist in a way she was all about 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. she was a super woman. >> reporter: their mom embraced adventure. >> one time mom and i went. just the two of us. i hadn't been horse back riding for a while. i didn't want to go five or six miles. she said i found a trail that is eight miles and by the time it ended it was 16 miles. 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. but their dad was not all business all the time. >> in the traditionally motherly roles he wasn't afraid to be mr. mom. >> reporter: the mueller kids said their parents fit one another perfectly. >> you make a point of every night, to try to do something nice for her. >> he was so proud of her. they talked all the time. any type there was a disagreement about the dishes weren't done. they would talk about it until they were completely resolved and the next second, they would be all over each other and perfectly happy again. >> reporter: it was a happy weekend at the mueller's colorado cabin. may 3rd, 2008. now that leslie was no longer working she was spending 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 like that around the house. >> so was this a typical weekend in colorado? >> yeah. >> it was just alex, then, 14, up with his parents on this trip. >> reporter: 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. 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. ongoing for the hike. >> reporter: fred and leslie headed off with her dog gracie, a border collie pup. >> i think she was only six months old. >> rambunctious? >> for sure. she's the type of dog that when the ceiling fan would be going, she would try to jump up and 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 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 happened 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? too soon to know. >> reporter: the hunt for answers would start with a frantic search. >> at the waterfall, she fell and they can't find her. >> his wife? >> yeah. >> reporter: where was leslie mueller? and did she survive? >> all of a sudden i hear yelling and yelling is coming from downstream. >> reporter: when dateline continues. orter: when dateline continues. with dupixent, show off your clearer skin and less itch. because you have plenty of reasons to show off your skin. with dupixent, the number one prescribed biologic by dermatologists and allergists, you can stay ahead of your eczema. it helps block a key source of inflammation inside the body that can cause eczema to help heal your skin from within. many adults saw 90% clearer skin. some even achieved long—lasting clearer skin and fast itch relief after first dose. serious allergic reactions can occur that can be severe. tell your doctor about new or worsening eye problems such as eye pain or vision changes including blurred vision, joint aches and pain, or a parasitic infection. don't change or stop asthma medicines without talking to your doctor. ♪♪ show off to the world. ask your eczema specialist about dupixent. only purple's gel flex grid passes the raw egg test. no other mattress cradles your body and simultaneously supports your spine. ask your eczema specialist memory foam doesn't come close. get your best sleep guaranteed. save up to $800 during our memorial day sale. visit purple.com or a store near you alex mueller was alone at his family's vacation cabin in colorado. 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 sated to your mom as she was leaving the cabin? >> see you later. >> just a normal of course i'm going to see my mom in an hour. >> exactly. not nothing really memorable. >> and so then, there is a whole period of time they are gone. what's the next thing you remember? >> so, reading, kind of hanging around. i think the first time i noticed, it was getting a little late. dark. no one should be hiking when it is 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 is 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 at the creek, the owner of the house, justin sparks, was the first to call 911. >> he told us she's in the river. she fell and they can't find her. he is frantic, of course. >> 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, physicians assistant and ems volunteer michael was on duty. >> a call went out over the radio for a female drowning victim. >> reporter: he headed over to the base of the trail. there, he ran into fred. >> he comes barreling down at a very high rate of speed. slams on his brakes. slams let's go, let's go. >> reporter: the ems responder noted this man could also be injured. fred's face was scratched up. >> he has superficial lacerations. i take a minute to make sure this is not my second victim. to make sure he is okay. he ensures me he is fine. >> reporter: 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. we get back in the jeep. upstream or uphill. >> reporter: after another stop, they found the right place and hiked toward the creek. >> all of a sudden i hear yelling. coming from downstream. >> reporter: it is the homeowner justice sparks. michael took off toward him. >> there was mrs. mueller dressed in a lime green jacket floating face up. he found her. i believe he used the word pinned under the log and face down. >> reporter: leslie had no pulse. but he thought there was still hope she would be revived. fred had caught up, towering over them from the creek embankment. >> he says is she dead? i tell him it is too soon to know. >> reporter: he 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, deputy casey. >> we had officers responding. the ems personnel. fire personnel coming with the fire trucks. >> reporter: dispatch put a call into local sheriff ron bruce. >> we had gotten a report of a drowning. they said they would keep you advised. >> reporter: a group of medical responders went 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 ms. 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 had been gone three hours. >> were you worried? >> not really worried as in something happened to them. it was weird they would stay out past dark. >> reporter: it was past 8:00 p.m. when his dad got home. without his mom. >> it is my dad. and, the deputy. and they come in. it is kind of a shock to see when you are expecting somebody. you see strangers coming in, instead. >> what do you think when you see that? >> not a whole lot of time. you go into shutdown mode. >> reporter: alex recalled husband dad seemed like he was in shock. >> he was very disheveled. had been crying a lot. and he gave me a big hug. and that was how it broke. >> i can't imagine getting that news when you just thought your parents were going for a quick hike. >> disbelief really. the whole thing 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 and 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 have dotted the is and crossed the ts . we are dealing with the death of a woman. >> reporter: then fred and alex headed back to the empty cabin and the home that had been full of such happy memories. they endured the longest night of their lives. >> we stayed together in the same night. >> did your dad sleep? >> it was a long night. >> reporter: 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. took a few of me. >> reporter: 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. >> reporter: and he is very clear on who is to blame. >> it was that dog tangled up in her legs is what i think it was. >> reporter: what would police think of that? when dateline continues. think of that? when dateline continues. then i found a chance to let in the lyte.” discover caplyta. unlike some medicines that only treat bipolar i, caplyta is proven to deliver significant symptom relief from both bipolar i & ii depression. and in clinical trials, movement disorders and weight gain were not common. caplyta can cause serious side effects. call your doctor about sudden mood changes, behaviors, or suicidal thoughts right away. anti-depressants may increase these risks in young adults. elderly dementia patients have increased risk of death or stroke. caplyta is not approved for dementia-related psychosis. report fever, confusion, or stiff muscles, which may be life threatening, or uncontrolled muscle movements which may be permanent. common side effects include sleepiness, dizziness, nausea, and dry mouth. these aren't all the side effects. in the darkness of bipolar i & ii depression, caplyta can help you let in the lyte. ask your doctor about caplyta. find savings and support at caplyta.com. only purple's gel flex grid passes the raw egg test. no other mattress cradles your body and simultaneously supports your spine. ask your doctor about caplyta. memory foam doesn't come close. get your best sleep guaranteed. save up to $800 during our memorial day sale. visit purple.com or a store near you ah, these bills are crazy. she has no idea she's sitting on a goldmine. well she doesn't know that if she owns a life insurance policy of $100,000 or more she can sell all or part of it to coventry for cash. even a term policy. even a term policy? even a term policy! find out if you're sitting on a goldmine. call coventry direct today at the number on your screen, or visit coventrydirect.com. it's hard to run a business on your own. make it easier on yourself. with shopify, you can have your inventory, payments, and customers in sync across all the places you sell. start your journey with a free trial today. fred and leslie mueller's daughters, amanda and ariel, were hundreds of miles away from colorado when it happened. their dad had to break the terrible news to them by phone. he said, i'm so sorry. i'm so sorry. and i said, what happened? and he said, we were hiking. i was trying to take her picture. she fell. and i remember saying, but she's going to be ok? and he said, no, she's dead. and i kind of lost it. i started crying terribly. and he said, i'm so, so sorry, mandy. what did your dad say to you when you got him on the phone? 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 in my life >> thati don't think i asked hi what happened. you don't want to hear details. i could easily say it was the worst day of the life i found out about my mom. and, the only detail that matters is she was gone. >> reporter: the tragic details, however, were the business of hensdale county sheriff ron bruce. he and his small office had the huge job of patrolling more than 1100 square miles of potentially dangerous wilderness and wildlife. >> should they have not gone to that area? >> no. it was perfectly fine. i think he related it was something of an idyllic day. >> reporter: the day after leslie died, sheriff bruce stopped by the mueller's cabin to get a more precise account of what happened. bruce's undersheriff and a state investigator talked to fred. >> you know, shouldn't have ian taken her up there. it's all my fault. >> reporter: the conversation at the mueller's kitchen table was recorded. >> we started taking photos. she took a few of me. i took a few of her. >> reporter: fred described how that kodak moment went wrong. >> i suggested she take a picture with her dog. it's a border collie. extremely skittish dog. she looks at me and i take her picture and we think everything is cool. and, i think like a bird kind of flutters by. >> reporter: fred says the rambunctious border collie got startled. >> the dog just jumps out as she is turning, it's like her feet went out from under her. like it happened in slow motion in front of me. she falls forward and i remember lunging forward to try to get to her but i was probe seven feet from her. >> reporter: fred says he witnessed leslie free fall. >> 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, and just just crumples and slides like mush into the channel. i should have just jumped in. >> reporter: fred said he lost sight of leslie in the water so he ran down toe where he thought the current would take her. said he got scratched up as he stumbled up and down the embankment. >> i must have tripped, i don't know. a few times. i'm sure i hit something coming down a few times. >> reporter: he told how he had left the camera with the last images of his wife behind. >> i imagined 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. >> hauled butt down to justice's house. i'm honking and screaming at him. i think my wife is 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 walk through on the scene. >> reporter: up at the scene, fred repeated how the dog seemed to cause leslie's fall. >> it was that 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 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 is 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 seats found near the ledge where leslie spent her last moments. >> all the alarm bells were going off. even to this day it gives me the chills. >> reporter: and a family worries about their grieving father. >> you just didn't know if he was going to do something crazy or ever get over this and be able to move on. >> reporter: when dateline continues. >> reporter: when dateline continues. ime. i hear that. that's why we protect all your vehicles here. but hey...nothing wrong with sticking it to the boss. ooooh, flo, you gonna take that? why would that concern me? because you're...the... aren't you the..? huh...we never actually discussed hierarchy. ok, why don't we just stick to letting dave know how