>> one of the most extraordinary cases in lapd history. >> toto, were not in kansas anymore. >> a newlywed murdered months after her wedding. >> as she walked away, she gave me a big smile and and i lived in that smile for years. >> and all the time episode the killer was hiding in plain sight. >> no indication she was ever spoken to? >> no. >> then a new detective took a look at an old lead. >> he just said it's a match. >> a person no one would have ever suspected of murder. >> we were going to end this. >> was suddenly suspect number one. >> perfect murder. almost. ♪ ♪ ♪ >> hello. welcome to "dateline". she was a new bride married just three months, then she was found murdered. what happened to her remained a mystery for decades partly because police told us the thief must have killed her during a break-in gone bad. they discovered it wasn't a murder, but a suspect whose trail right to their own front door. here is josh mankiewicz with " the smoking gun. " >> february 1st, 2009. the detective arrived before dawn at the los angeles police department's van nuys station. >> i was tired. i was tired. >> he had hosted a super bowl party the night before and the beer had flowed freely. >> that seemed to be a good day to have a cup of coffee and caught up on my reading. >> a couple of aspirin? >> maybe. >> he reached for a file sitting on his desk for months. the file of sherri rasmussen. shot to death in her condo a few miles from where he worked. >> it was one of the most horrific crime scenes. i said this guy met a horrible ending. >> just as troubling, sherri rasmussen was murdered a generation ago. february, 1986. meaning the odds of catching her killer were slim to none. >> memories fade. evidence has to be relocated. so it's obviously an uphill battle. >> uphill battle does not begin to describe it. the cold case the detective opened on that bleary-eyed monday morning would lead him on a chase of a lifetime and shake the foundations of the lapd. dates back to 1986 and a battle for the truth by the parents of a young bride. >> we miss her every day. >> those parents are nels and loretta rasmussen. >> doesn't make any difference what day it is. it's a pain that is always there. there's no cure for it. >> who would want to kill sherri rasmussen? she was hard-working, caring, and popular with her coworkers. trained as a nurse, sherri was director of critical care at a large local hospital. >> we are implementing the people difference program. >> it was a devastating day. she was 29 years old and just in the prime of her career. >> althea kennedy was sherri's boss at the hospital and had originally hired her. >> we couldn't believe it. first of all, like how could someone do this? people crying. people upset. i mean, the hospital was like a tomb, you know? so, the loss was real palpable. >> sherri had just married three months earlier to john ruetten. >> where the happily married? >> unusually so. >> months after the wedding, john found sherri sprawled dead. he might seem a likely suspect, but john was cleared almost immediately. the lapd focused instead on evidence that this was a burglary that turned violent. >> this was no accident. >> yolanda mcclary was a retired crime scene investor investigator and was a consultant to "dateline. " >> multiple shots fired. shots fired at very close range. >> she has reviewed court records and media reports on this case. we returned with her to the actual apartment where sherri was found murdered to try to understand what happened. police think maybe the killer just walked in the open front door? >> they didn't find any forced entry, so, yes, they are assumg the front door was open and the killer just walked right in. >> right here where we are standing, is there some kind of confrontation? >> yes. this appears to be a struggle here. not just a struggle, but we also have shots fired at this point. we have one shot that clearly goes straight through this back slider and another shot that went through sherri and then back out through the slider also. >> so, sherri is now wounded and she tries to get back downstairs? >> that would be correct. she is bleeding profusely and very wounded and she gets down these steps and actually it would appear she is trying to go out the door, or make it to that alarm box where there is a panic button. at that point, we believe that sherri went down in this foyer area, due to the fact that you could see marks in this, as well as broken fingernails from her hands. >> so, there is a tremendous fight going on? >> well, yes. the killer is actually dragging her back into this area and then the killer takes a vase and hits her in the head with it, knocking her out. then grabs the blanket, muzzles the gun, and does and does a close contact shot into the victim. >> so, that is an execution? >> that would be correct. >> as for a motive? it seemed to be in plain sight. just a few feet from sherri's body >> they found vcr and a disc player that was stacked one on top of the other in the front door. >> as if somebody was about to steal them? >> yeah, giving the indication this was a burglary or a home invasion gone wrong. >> sherri's purse was missing, as was her new bmw, an engagement gift from john. there was no sign of the murder weapon, but detectives did recover two. 38 caliber slugs and something else that caught the detective's attention. >> on the inside of sherri's left arm, they found a bite mark. a crime scene analyst went ahead and she swabbed that for saliva that could pertain to the killer. >> saliva that contained dna from whoever bit sherri. remember, this was 1986, years before dna technology testing would arrive, which could link a suspect to a sample like this one. so, back then, the dna wasn't much help. but the swab was carefully package and bundled with all of the other evidence. for now, detectives didn't have much else to work with. no eyewitnesses. no usable fingerprints. no clear motive, except for theory that this was a botched burglary. >> by the level of violence that occurred in this residence, the theory was that it was a man or possibly two men that had entered the residence to do a burglary or a home invasion that had not gone completely wrong, murders the victimet to cover up the crime and then fled. >> gone wrong because sherri somehow surprised them. they panicked, shot her, and then fled. the theory seemed to make sense, especially since sherri had no apparent enemies, certainly no one who want to kill her, or so they thought. >> coming up. >> we went to sherri's office and said if she couldn't have john, nobody could. >> when "dateline" continues. for the chance at clear or almost clear skin. it's like the feeling of finding your back... is back. or finding psoriasis can't deny the splendor of these thighs. once-daily sotyktu is proven to get more people clearer skin than the leading pill. don't take if you're allergic to sotyktu; serious reactions can occur. sotyktu can lower your ability to fight infections including tb. serious infections, cancers including lymphoma, muscle problems, and changes in certain labs have occurred. tell your doctor if you have an infection, liver or kidney problems, high triglycerides, or had a vaccine or plan to. sotyktu is a tyk2 inhibitor. tyk2 is part of the jak family. it's not known if sotyktu has the same risks as jak inhibitors. find what plaque psoriasis has been hiding. ask your dermatologist about sotyktu for clearer skin. so clearly you. sotyktu. after advil: let's dive in! but...what about your back? it's fineeeeeeee! 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[sfx: video game] emergen-c crystals. >> the year was 1986. crack was hitting los angeles, and the city of angels had become a violent place. the murder rate would hit 831 killings that year. nearly three times the amount 30 years later in 2016, and the lapd was stretched very thin. >> this was a time where homicide was just booming in los angeles. >> miles corwin is a best selling author who has written several books about the lapd. >> it's kind of a perfect storm of problems. you had the proliferation of high-powered weapons and crack cocaine hitting the streets, a tremendous homicide rate and detectives are overwhelmed. >> in february of that year, cops had their hands full with an especially heinous crime in the san fernando valley that was sprawling. 29-year-old sherri rasmussen had been brutally beaten and shot in her own home. no suspects and few clues. then a couple of weeks later, a possible lead. former criminal variation yolanda mcclary was a consultant for nbc news. >> in the same vicinity, another woman was approached in her residence by two males at gun point, also involved a home invasion robbery situation, so police, early on, thought there was a possibility these two men might have something to do with the murder. >> a composite sketch was released of the 2 men. the dna collected at the crime scene was useless, at least right now. police collected it any way. why? >> at crime scenes, if you know there's possible evidence on anything, you're not going to leave it behind. so, it was great forethought on their behalf actually to recover it. >> detectives scoured the condo and the entire complex. the only thing apparently stolen was from the garage, sherri's car. and that was recovered just a mile away from the crime scene with the keys still in it. the only other thing missing, sherri and her husband's marriage license. it seemed an odd thing to steal. cash, computers, and jewelry were not touched. but that wasn't the only thing that struck sherri's family and colleagues as strange. the crime was especially violent for a two-bit burglary. >> it just seemed a little like overkill. >> sherri's boss at the hospital, althea kennedy, had to review sherri's autopsy report for insurance reasons and she was struck by what she saw. >> i thought, wow, she really put up one heck of a fight. which wasn't real surprising, because sherri was tall, athletic, and i'm sure wouldn't go down easily. >> the lapd theory back then was that there were two men robbing the house and so, presumably, sherri would have fought with two guys. does that sound like sherri? >> that part didn't make sense to me because two men and two guns seemed weird. >> because sherri wouldn't begin a fight with two guys who were armed? >> i wouldn't think so. >> what about with a woman? >> i think she would have taken on a woman. >> we would really like to know what happened. >> sherri's parents knew it it was a burglary. weeks before the burglary, sherri had several strange encounters. one as she dined at a restaurant and thought a woman was watching her. >> she said she has eyes that can see right through you. >> scary eyes. >> there was also a run-in at the hospital where sherri worked. >> she went to sherri's office and said that if she couldn't have john, nobody could. >> most terrifying, an encounter in sherri's own home. and by now, she knew who the mystery woman was. >> she heard a noise and she looked up and there was john's ex-girlfriend. >> how did she get in the house? >> we have no idea. >> john's ex-girlfriend appeared to be stalking sherri. yet sherri never mentioned the woman's name to her parents. instead, she told them not to worry. >> she told me, i want to see if i can't work this out myself. >> that conversation happened during a dinner celebrating sherri's 29th birthday. afterward, her parents should sherri to the airport. >> as she walked away, she turned and gave me a big smile, and i've relived that smile for years. >> less than three weeks later, sherri rasmussen lay dead. the rasmussens insist that early in the investigation, they told the lead lapd detective about sherri's troubling encounters with john's ex-girlfriend. >> i told the detective not once, but probably 15 to 20 times. and he said, the trouble with you is you've been watching too much tv. >> coming up -- old evidence offers new clues. >> the suspect made it appear to look like a burglary. they staged it to mislead the initial investigation in 1986. she was executed. >> when "dateline" continues. (carolers) ♪ it's all good - just a little awkward. ♪ (soloist) think we'll wrap this up. (vo) for a limited time, turn any iphone in any condition into a new iphone 15 pro with titanium and ipad and apple watch se - all on us. that's up to $1700 in value. only on verizon. >> years had passed and no arrests had been made in the brutal 1986 slaying of nurse and newlywed sherri rasmussen. killed in her los angeles condo. the trail kept getting colder. in 1993, sherri's parents offered to have the saliva sample the bite mark for dna, and even pay for it, but the lapd declined. >> she said we don't have a suspect. if we had a suspect we would have something to match. >> the case sat for another decade. but then in 2004, the lapd was conducting cases on cold cases and one of them was the murder of sherri rasmussen. it took two months to find that saliva sample -- buried in a refrigeration unit. the envelope was tattered, label torn, but the saliva was still inside and the dna was just enough to blow this case wide open. >> in that lab report, it indicated that the suspect that had bitten sherri rasmussen during the struggle was a female. >> a woman. not two male burglars, as the original detectives had suspected all those years. but it would take a few more years before investigators began to understand what that crucial dna test result meant. it was now 2009, and the case was cold once again. 23 years it sat with no apparent leads, no suspects, and no answers for the rasmussen family. then came that monday after the super bowl when detective jim nuttall started peeking through that old case file and made a remarkable discovery. the dna test that had been conducted on that bite mark back in 2004. once the department realized a woman was involved, why did it take four years until you finally picked it up? what was the department doing in the interim? >> from what it appears, investigators may have followed the initial theory of this crime, that, in fact, it was a burglary. >> and that there was a woman involved in the burglary? >> that there was a woman involved in the burglary. looking back now in hindsight, it was an opportunity that may have slipped through our hands as an organization. >> but now nuttall took a closer look at the crime scene photos and began to develop his own very different theory. remember, sherri rasmussen was shot at point blank range after a violent struggle, and despite the stereo equipment stacked by the front door, very little was actually stolen. >> the suspect made it appear to look like a burglary. they staged it to mislead the investigation in 1986. she was executed. >> in other words, someone had wanted sherri rasmussen dead. so now, nuttall dug deeper through the file looking for names, female names. >> we had five women that would have had access to sherri and perhaps at least some of them may have had a motive to harm her. three of them we eliminated almost immediately for insufficient motive. >> but there were still two names left. one of them was a coworker. >> a woman named debra that worked with sherri rasmussen in the glendale hospital. this person of interest was later placed by sherri rasmussen in an official capacity and problems followed almost immediately after that. >> so, there was bad blood between them? >> there was a motive. >> debra had moved to northern california. nuttall asked local law enforcement to watch her and secretly try to snag a sample of her dna for comparison testing. in the meantime, nuttall learned more about the second woman. he contacted john ruetten, sherri's former husband and now remarried and living in san diego. >> john involved he had been involved in a dating relationship with stephanie lazarus. >> stephanie lazarus -- that was the other name on the short list of suspects. nuttall pressed ruetten for more on their relationship which had started when they were both students at u.c.l.a.. they dated on and off until john got engaged to sherri. but even then... >> even though you're convinced the relationship that john had with stephanie lazarus overlapped with the relationship he had with his wife? >> we know from john that there was at least on one occasion where he was engaged that he was intimate with stephanie lazarus. there was a love triangle and stephanie lazarus had deep feelings for john ruetten, and may have had a motive to harm sherri rasmussen. >> was sherri's killer a scorned lover or a jealous coworker? >> we had two women on the list who, in our opinion, had a motive to harm her. >> debra, the nurse, and stephanie lazarus? >> correct. >> a few weeks later, cops in northern california tracked down debra and secretly scooped up a sample of her trash which contained dna. it was sent to the crime lab in l.a. for analysis and 72 hours later, came an answer. >> she was not the donor of the dna profile from the bite. >> that left just one possible suspect, number five on the list, john ruetten's ex-girlfriend, stephanie lazarus. nuttall called the rasmussens. >> we came home and there was a message on our phone from a detective that they wanted to talk to us. i thought oh, yeah, right. i thought it was just another false hope. >> this is detective nuttall? >> right. >> he said that they were opening the investigation. >> nels was upset with me. it was like, detective, where have you been for the last two decades. >> now nels rasmussen explained it all. how he told detectives back in 1986 that someone was stalking his daughter, sherri. a woman with crazy eyes. the ex-girlfriend of sherri's husband. nels had never known that the girlfriend's name was stephanie lazarus. but he did know something else about her. something very important and by this time, detective nuttall knew it too. >> he was very cautious of what he said. but he said that we would be hearing more from him. >> nuttall had ample reason to be cautious. because he learned that stephanie lazarus wore the same badge he did. >> we now have a los angeles police officer as a person of interest in a murder case. >> and you thought, i've bitten off more than i can chew? >> toto, we are not in kansas any more. that changed everything. >> coming up -- a top secret