this is "nightline." >> tonight, night terror. the image of a seemingly happy family shattered by murder. >> i went to bed as the 12-year-old kid with the happy life, i woke up to a police officer telling me that my mother died. >> a husband accused of killing his wife. what he claims happened while he slept. >> are you kidding me? sleepwalking? >> was it a case of a sleepwalking killer? or something else? >> scott did you knowingly kill your wife? plus, following the clues from that fateful night. now the new prison interview. >> have your thoughts changed at all about what you believe happened that night? did you know prilosec otc can stop frequent heartburn

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you're about to hear from a man who's been sitting behind bars for more than two decades, claiming he doesn't remember killing the woman he loved. now giving a revealing new interview to "20/20" coanchor amy robach.

>> it just didn't seem real. i'm not sure that even until i got to the police station that i was 100% convince d that yarim was dead. >> what makes you think i did it? i'm not sure what makes you think that. >> the neighbors there watching you do it, that's why. >> authorities say scott stabbed his wife over and over, then held her head underwater. >> did you love your wife? >> oh, yes. oh, yes. loved her a great deal. >> >> reporter: the trial was a sensation, not because of the crime itself but because of scott falater's defense. >> kind of smirked, are you kidding me, sleepwalking? >> an arizona man set out to convince a jury he stabbed his

wife 44 times while sleepwalking and doesn't remember a thing. >> they're pretty rocks, this is why people come here. there's our driver. >> reporter: the falater family is living in arizona. scott falater is a successful engineer, he's working at motorola. yarmla is in charge of the kids. they've been happily married over 20 years, scott calls her "yarm" for short. >> january 16th. it was a typical thursday for my family. i recall having family dinner after dinner, i went and worked on the computer, then the kids went to bed at 9:00. >> it's been a long day at work.

now his wife wanted to go fix the pool filter at 9:00 in the evening. >> the old ring was old and kind of stuck. he tries to dig it out of the pool pump. he's not able to get it all out. >> my wife was asleep on the couch with "e.r." on television. i woke her up, kissed her good night, apologized for not fixing the pool filter, said i'd fix it the next day, went to bed. >> stephanie and reid live next door. >> greg and i were getting ready to go to bed 10:00, 10:30. and then i heard moaning or crying or something. and then i told greg, i think it was something outside. >> what the neighbor sees is a body of yarmla lying there. he thinks maybe this is someone drunk and passed out. some time passes. scott then comes out onto their backyard. he grabs her by the arms, over her head, and drags her to the

edge of the pool. he then seems to roll her body into the pool. >> we thought he was splashing her and trying to wake her up. then i remember greg running in, "oh my god, he put her head underwater, she's in the pool, but now he's holding her head under the water." >> officers arrived on scene. we went over the wall. >> as soon as i picked her up and saw the water go dark red, you know, that's when my heart did sink. >> that's when i first saw scott falater. he stepped in, and from what i recall, almost immediately, i recognized scott falater at the top of the stairs wearing a crisp white t-shirt, red flannel pajamas, and he made remarks, what's going on, what are you doing in my house, why are you here?fud at

first. i kept asking, what is going on? all they would yell is, shut up, get down. they kept asking how many people were in the house? four. >> we asked how many people? he said four, two kids, his wife and himself. i observed his wife in the pool as i jumped over the back wall. >> i went to bed as a kid in a happy family, woke up to a police officer telling me my mother died. >> scott falater says in those early moments he's confused. he doesn't seem to realize what's happened to his wife or that he may be responsible. >> how does he think i did it? i don'kn wyothk at.welleighborsw kill your wife, that's why. >> a lot of suspects might say, no way, you got the wrong way, i would never.

scott just keeps saying, "i don't remember." >> i'm sorry, i don't remember doing it. >> you have blood on you. >> what blood? >> all over your neck. >> strangely, there is no blood on scott's crisp white shirt or red pajama bottoms, but detective norman sees some on his neck. >> here? i didn't know there was blood on me. >> scott is arrested. he's charged with first-degree murd murder. and if convicted, he is facing the death penalty. >> michael, are you aware of the fact that if your father is convicted of first-degree murder, that the prosecutor could ask for the death penalty? >> yeah. >> have you prepared in your mind for that prospect? >> not really. >> i can't see my father killing my mother intentionally. that is not like my father. my father was not a violent

person. >> good afternoon to all of you. this individual here, the defenda defendant, in a sense enticed his wife into the afterlife. >> i'm the chief medical examiner. >> the medical examiner testified yarmla falater had 44 stab wounds. most of them were defensive wounds, some were fatal. >> based on what the medical examiner told us about the stab wounds, we believe once he had her near the pool pump, he put his left arm around her mouth so she wouldn't scream, then looped his right arm around her shoulder and began to stab her. she knew what was going on around her, and she could not do anything about it. >> then he had his bombshell witness, the next-door neighbor.

>> i saw a person laying on the ground. >> greg testifies he sees scott putting on gloves as he approaches yarmla's body lying next to the pool. >> he moved her legs around to the side, he knelt down behind her and pushed her into the water. >> scott's family is totally bewildered. this is not their mild-mannered, nonviolent son or brother. until they remember that scott used to sleepwalk as a child. >> one time he came down the stairs, and he was probably over 15 or 16. and he was stark naked. and the next day you'd ask him about it or talk to him about it. he had absolutely no idea that this happened. >> his sister recalled a time he was violent during a sleepwalking "the nit

show." of behind me. applaudingbual and i said, scott, what are you doing? he didn't answer me. and then he started walking toward the backdoor. >> she thought, oh, he's sleepwalking. so she ran in front of him to lock the door leading out from the kitchen to the outside. >> when i did that, i brushed against his shoulder. he turned around and grabbed me by my shoulders and tossed me. he looked just so angry. he looked almost demonic. >> the defense tried to say that this was not scott falater acting consciously, that this was a monster emerging from the depths of his unconscious, an irrational, inexplicable eruption of a man who had come enormous pressure. >> the defense brings in two heavyweight sleep experts.

>> you have conducted an evaluation of scott falater in this case, have you not? >> very, i have. >> and have you reached an opinion regarding whether he was sleepwalking at the time he killed his wife? >> it's my strong belief that that was the case. >> you have an opinion whether scott falater was in a sleepwalking state when he stabbed his wife? >> in my opinion, he was. >> scott falater says he remembers none of this, but he and his sleepwalking experts speculate as to how this killing might have happened. >> reporter: sleep deprived and stressed out from problem at work, scott crashes into bed and then rising in a sleepwalking state. >> he gets the idea, i'm going to fix the pool pump again. >> yarmla interrupts him in his sleepwalking state, which the experts will tell you is a

dangerous thing to do. >> he sees her not as his wife but as some threat that his instinct wall brain responds to while he's asleep. >> that is when scott falater attacks. >> officers who search the home tell the jury how theytt a clue that could easily have been overlooked. >> what did you find? >> a black plastic trash bag. >> and anything in and around this black plastic trash bag? >> a tupperware container that had articles of clothing within that looked odd, and on closer examination i noticed they had blood stains on them also. >> that's where they found the clothes that he had been wearing, apparently, when he stabbed her. >> so what did you find inside of this tupperware container once you opened it? >> that was the murder weapon, voila. everything we're looking for. we hit the jackpot. >> the prosecutor calls his own

sleepwalking expert to the stand, dr. mark pressman. >> if your experience, do sleepwalkers conceal objects, generally speaking? >> sleepwalkers may misplace items, but to my knowledge, sleepwalkers never hide something. these items were not only hidden, they were packaged neatly. >> for the prosecution sleepwalking expert, the most compelling evidence that scott falater was awake came after he stabbed his wife. he returned to yarmla's body and dragged her over to the pool, held her under. a second act of violence. the only way that sleep specialists think that violence can happen with a sleepwalker is that somebody confronts them, physically confronts them, gets in their way. that's clearly impossible on the second episode of violence. >> he's got the weapon. he's got an eyewitness. there's just one thing he hasn't got, a motive. and suddenly it seems to appear, a phrase scott falater used,

unforgivable sin. >> whatever this unforgivable sin is, he can't wait to be rid of her. find your rhythm. your happy place. find your breaking point. then break it. every emergen-c gives you a potent blend of nutrients so you can emerge your best with emergen-c. ordinary tissues burn when theo blows. so dad bought puffs plus lotion, and rescued his nose.with m puffs brg hi stn and relief. a nose in need deserves puffs indeed.

♪ now the courtroom showdown reaching a tipping point. was the father too awake, owi? >> all rise, please. >> next witness will be the defendant, scott falater.

>> did you knowingly kill your wife? >> objection, asked and answered. >> overruled. >> no. no, not at all. i couldn't knowingly kill her. no one deserved it less than anyone i know than her. >> the prosecutor, juan martinez, seized on a remark made in the notes of a psychologist who had interviewed scott falater in jail. a phrase scott used during their conv"unfgiest it? do. >> jnhe bigstthis, that somehow yarmila had committed some kind of a horrible something, suggesting unfaithfulness by yarmila. he kept grinding on that for motive. >> when you say unforgivable sin, it suggests she had cheated on scott falater, but that's

really not the case, is it? >> i'm not suggesting anybody committed the sin of adultery. i can't get into mr. falater's head and look to see what he considered to be an unforgivable sin. it is his phrase. >> so when you uttered the word unforgivable sin, what did you mean? >> i felt that perhaps i had committed the unforgivable sin by killing yarm. >> during the six-week trial, the jury heard testimony from 52 witnesses. 180 court exhibits were marked and put into evidence. but it took only eight hours of deliberations before the jurors sent word to the judge they had a verdict. >> we, the jury, duly impanelled and sworn in the above-entitled action, upon our oaths do find the defendant guilty of murder in the first degree. >> it was a traumatic moment for all of us.

>> judge rhinestein had to decide whether or not the death penalty was going to be imposed >> i accept the responsibility that it was i that killed her. i'm certainly sorry for the pain that yarm must have felt that night. >> in the end, he was sentenced to life in prison. serving that life sentence in an arizona prison. have your thoughts changed at all about what you believe happened that night?

>> i cannot swear on a stack of bibles that i was sleepwalking, all i can say is i do not know what happened. suffering that this whole thing caused. and it's on me. >> hey, mike. >> hey, how are you, dad? he's still my dad. and i hope to always have that relationship with him. whether he's in prison or he's out. >> you know what i miss was when we would go out on christmas eve and buy stuff for mom. remember that? >> yeah. >> yeah, i miss that stuff. being out. just being with you guys. >> yeah. >> 20 years later, when i think of scott falater, it is still a complete and total mystery to me as to what the hell happened that night. >> i can't tell you for sure whether the man was asleep or not. >> i think we all have a sense that we are capable of performing as human beings, acts of great dignity, and

occasionally, acts of great violence. and scott falater was a figure capable of both. >> we'll be right back with the final note. ♪ ♪ (quiet piano music) ♪ ♪ comfort in the extreme. the lincoln family of luxury suvs. want to brain better? unlike ordinary memory supplements— neuriva has clinically proven ingredients that fuel 5 indicators of brain performance. memory, focus, accuracy, learning, and concentration. try our new gummies for 30 days and see the difference. lactaid is 100% real milk, just without the lactose.

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♪ finally tonight, a wconvict. high-profile lawyer juan martinez voluntarily gave up his law license last year after denying allegations he committed ethics violations and he sexually harassed female law clerks in his office. that's "nightline." thanks for staying up with us. good night, america. have a great weekend.