>> there are a couple of cases that i've really carried with me. there's a woman that lost her life. it was so emotional. it was heartbreaking. >> reporter: a wife and mom dead >> my son just killed my wife. >> reporter: two separate calls, two separate stories about the same haunting crime. but only one caller was telling the truth. father versus son. >> i grabbed him. i said stop. he throws me to the ground. >> he's very good at making up stories. but that's not true. >> each is accusing the other of

the crime snt >> yes. >> and you have to figure out who the killer is. >> that's the problem. >> reporter: broken glasses, a blood. would investigators get it right? >> no one on our side of the family had any doubt. >> we may have the wrong guy in jail here. >> reporter: would a jury? >> it was a battle. both sides are coming guns blazing. >> reporter: i'm lester holt and this is "dateline." >> his story is all lies. >> any do it. >> reporter: who will you believe? tonight, dennis murphy with "true lies." >> reporter: bill kyne knew he was a lucky man. the single dad with five kids was getting a second chance at love. >> she was the most wonderful lady i'd ever met. >> reporter: he first set eyes on her at a nail salon, a business she ran with her twin sister. >> and they're standing in front of this big neon sign that says, "nails." and i said, "do you all do nails here?" and they just looked at the sign

and then looked at me and said, "yeah." >> reporter: her name was diane. a vivacious blonde, with a ready smile. >> he saw diane through the window, so the next weekend i went to get my nails done. >> reporter: rebecca kyne is bill's youngest child. >> gave him an excuse to meet her. >> rebecca you were being used as bait. do you realize this now looking back? >> oh, i was fully aware at the time. >> reporter: it was a light moment and just what bill needed. only eight months earlier, he'd become a widower. >> my wife, krista, she fell in the middle of the night. they say she hit her head and she drowned in the pool. i pulled her out of the pool easter sunday morning in 2000. i pretty much fell apart. and there i was a single dad, trying to raise them and, you know, keep the family going. >> he loved my mom. he loves her to the moon and back and then he lost her. he was just lonely and you could see it in him. and my brothers were definitely egging him on to get out and meet somebody. >> reporter: and in diane, bill met somebody special. >> diane comes into the picture

and he has this beautiful woman and now she's taking care of him. he was in love with her. he needed that. he needed her. >> she was actually what i consider by dream girl. blonde hair, blue eyes, and just a beautiful person inside and out. >> what did she like to do? what tickled her? >> she loved to raise animals. she bred yorkshire terriers. we loved going to nascar races together. she had just a big heart and she would reach out to family and friends, anyone who was in trouble, they could always count on her. >> reporter: and the person who counted on her most was her son kevin. >> i'm an only child. i was actually -- through my whole childhood was raised by my nana. now my mom, she worked full time and was a single parent. >> reporter: kevin could be a handful but he was always a bit of a mama's boy and diane doted on her young son. >> me and my mom every day when we woke up, every night before i'd go to bed, we'd say we love each other. i mean, we loved each other immensely.

we were best friends. >> reporter: things moved quickly for diane and bill. kevin thought they just seemed right for one another. >> he was a kind person. he did do a lot for my mom. he gave her what she wanted. and they lived a happy life. >> reporter: bill and diane married in 2002. kevin was 15 years old when he walked his mother down the aisle. they moved into bill's home on a quiet cul de sac in seminole, florida, near st. petersburg. a solid neighborhood. good schools. for the first time, kevin had a steady male role model in his life. >> so how was kevin fitting into the picture here? >> kevin was fitting into the picture quite well really. he really took to me more than anyone else that diane dated with, she told me that. and you know, we got along very well. >> reporter: kevin appreciated bill so much, he wanted to take his name. >> he wanted his name to be the same as his mom and i. and i was very proud of that. >> reporter: so, what's wrong with this picture? not much.

kevin got along fine with bill but joining a big family with five kids was a challenge. he didn't always fit in. there was tension, and a lot of it swirled around the new baby of the family, young kevin. >> you could tell he was raised as an only child because he was all about himself and all about his way all the time. >> reporter: but, kevin's cousin tanya says the kyne kids didn't make things easy for their step-brother. >> the kids weren't accepting him at first. you know, they were mean and -- >> kevin felt like an outsider? >> a little bit, yeah. i think it was a lot of friction in the house. >> reporter: in the summer of 2010, things in the kyne house were tense and coming to a head. kevin, now 23, was jobless and still living at home. and then he had brain surgery to remove a benign tumor. he felt he needed time to recover but bill and diane were ready for the next chapter of their lives and his. >> we had actually been talking a long time about buying our dream home.

diane and i wanted to get out on our own, start our own life together. we were looking for a place of our own. >> but kevin comes too. >> no, you're 23 years old. it's time for you to be on your own. >> i needed to get out. we all knew that. and i wanted to. they wanted the house to themselves. i wanted to be on my own, too. i don't wanna live with my parents the rest of my life even though we're extremely close. >> reporter: on august 15, 2010 thoughts of dream homes and moving out faded into the routine of a hot florida sunday. bill mowed the lawn and cleaned the pool. kevin was looking forward to the nascar race and sprawled out on the couch. diane settled into the master bedroom. >> reporter: it happened a little before 2:00 p.m. a desperate call for 911. >> help me, please. >> please stop. >> ok, calm down, so -- >> he killed my mom. >> reporter: then, moments later another call. a different voice. >> oh, no, diane.

>> ok, they're on their way, alright? >> i don't think she's breathing. oh please. >> sir? >> be quick. >> reporter: something unspeakable had happened in the kyne house. a senseless, violent act. a mystery with lots of clues but no easy answers. >> it's almost like a agatha christie mystery, or something, where there's only three people there, and one of them is dead. so the killer has to be one of the other 2. >> reporter: but which one of the other two? that was the question that would haunt police. when we come back. >> it's a difficult case. >> reporter: the evidence at the scene. >> there's broken glasses and a shoe. >> reporter: who would it point to? both father and son tell their stories down at the station. >> i said, "kevin stop!" he grabs me and he throws me to the ground and takes off running. >> he's very good at making up stories. but that's not true.

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911. is this a fire, police or medical emergency? >> reporter: the 911 operators in pinellas county, florida, are used to dealing with life and death emergencies. but this one was different. diane kyne was dead. her husband and son were both distraught and both making frantic calls. first, kevin. >> my dad's trying to kill me. help me, please. he's outside of my house. he's choking me. >> okay, calm down. >> he killed my mom. >> stay on the phone with me. >> i can't hold on much longer. >> reporter: and then, bill. >> my son just killed my wife. he and my wife were arguing and he was choking her. >> where is your son?

>> he -- he ran out the door. >> reporter: two calls from the same location, just minutes apart. kevin kyne and his step-father bill each accusing the other of murder. >> oh, please. >> sir? >> be quick. >> reporter: "tampa bay times" reporter curtis krueger says the competing calls were even more unusual because they were made in the heat of the moment. >> one person, presumably, is calling and telling the truth. the other person has already figured out the story that they're going to use that's not true. that's pretty rare, and certainly quick and devious thinking by someone. >> reporter: father and son, one falsely accused of an appalling the other the real killer and a devious liar. the case would be a tough one. it went to veteran homicide detective jim beining. >> they both immediately accused each other as being the killer. >> so, you got to evaluate all these stories and figure out what's really going on. >> i do. it's a difficult case. >> reporter: first responders

found diane kyne's lifeless body face up in her own bed. kevin's loving mother, bill's loving wife, was just 49 years old. >> it appears that she is -- died from possible strangulation or asphyxiation. and there's some other things in the room. there's broken glasses at the bottom of the bed and a shoe. >> maybe most interestingly there was blood -- blood on the bed cover, blood on the victim, upper leg, huh? >> yes, the -- the victim had three small spots of blood on her leg. >> reporter: things were in disarray both inside the house and in the front yard. beining took a quick inventory. >> there are shirts in the driveway and the yard. um, pair of shorts. a phone was in the front yard. >> just those visual observations. any of that stuff explain itself to you about what might have happened there? >> not really, no. at this point, we've got to interview the -- the two people that were there. >> who do you begin with? >> begin with bill. >> reporter: detectives asked bill to come down to headquarters so they could get

his story. >> all right, bill, um, you do know why we're here tonight, right? >> his story is he and kevin were going to sit down and watch the nascar races on television. >> reporter: bill says kevin went to the master bedroom to talk to his mom. >> i hear her holler out, "kevin," in a loud voice. and probably five, ten, 15 minutes goes by, so i get up to go see what's going on. i push the door open and i see kevin on top of diane. i ran in, grabbed kevin from the back, pulled him back off of diane. he slammed me back into the armoire and he scooted out the door. i caught him at the kitchen. he was throwing me around like i was a rag doll. he shook me off again, took off for the door, he ripped the metal off of the door handle pulling it out so hard. >> so, now this tussle's going on in the yard. it's moved outside. >> now, we're out in the front yard. i grabbed him and -- and his shirt came off. at one point, i guess, his shorts came off. he had reached into his shorts before they came off, pulled out

a cell phone and he dialed 911. and he says, he's outside of my house. he's choking me. please help. >> i said, "kevin, stop! let's stop this!" he says, "okay, dad. okay, i'll stop." he grabs me and he throws me to the ground and takes off running. >> and he's gone. >> he's gone. >> reporter: bill then tried to catch his breath and collect his thoughts. his daughter rebecca found him head in hands outside the house. >> he looked so empty. when we got to my dad, he just -- he looked -- he looked like you just took the life right out of him. you took his life away again. and i just -- i broke down for him. i couldn't do anything but just reach out and hug him. >> reporter: with bill's story on the record, detective beining then talked to kevin to get his version of events. he said it started as just another sunday, with no hint of the tragedy to come. >> i was just kind of feeling a

little off so i laid down on the couch, was watching the race and stuff. bill tapped me on the head and said, "your mom needs to talk to you right now." and he actually tapped me on the scar. it was still scarred up and it hurt. and i said, "okay, well i'm sleeping i'm not feeling good right now. tell her i'll be a minute." and he came back again, did the same thing, "your mom needs to talk to you right now." i went towards her room and i pushed the door open. and as soon as i pushed the door open, he grabbed me from the back of the neck and put me in a choke hold. >> bill did? >> yes, sir. and he put me in a choke hold. and i was screaming, "mom, mom, mom, mom, please help me, anybody." and i saw my mom's face. her face was black and blue. it was -- it wasn't even blue. it was just black and it was absolutely horrible. and that's a mental picture that's going to be in the back of my mind for the rest of my life probably. >> you've been fighting on the front lawn. you've been calling to the neighbors for help. you're calling 911 for help. where does it go next? >> well, at that point, i finally got away from him. i did break free. i ran as fast as i could. >> are you running away from a murder scene? >> yes, sir. i'm running away from somebody that had just murdered my mother and somebody that was trying to

murder me. >> now, this story gets told a completely different way from bill. his version is that he comes into your mother's bedroom sees you on top of her, that you were on top of your mother killing her. did that happen, kevin? >> no, sir. he's very good at making up stories. but that's not true. >> you didn't kill your mother. >> no, sir, i did not. >> reporter: two distraught 911 calls. two dramatic stories describing a cold-blooded murder. only one of them could be true. >> reporter: coming up -- >> did you lie? >> i did not lie. >> reporter: a polygraph, dna -- and the curious death of wife number one. >> bill had a wife that drowned in the pool. >> reporter: was bill kyne becoming suspect number one? when "dateline" continues. difficult. if you have copd, ask your doctor about once-daily anoro ellipta. it helps people with copd breathe better for a full 24hours.

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each is accusing the other of the crime. >> yes. >> only one did it. and you have to figure out who the killer is? >> that's the problem. >> it's an axiom in your business that the spouse is always a suspect until they're not. >> yes. >> reporter: not only is the husband always a suspect, this husband had already been accused of killing his wife by his own son. so, detective jim beining started taking a hard look at bill kyne. >> are you finding out anything about bill? >> well, we did -- >> that puts him in the frame? >> sure. you know, bill had a previous marriage and they lived at the same home. and he had a wife that was, that drowned in the pool. >> that would interest me. >> sure it would. >> did it interest you? >> oh, absolutely. >> reporter: bill's first wife krista died in the middle of the night. there were no witnesses, but investigators believe she tripped, hit her head, and ended

up drowning in the pool. police ruled it an accident and bill collected on an insurance policy. >> do you know how much money was paid out on her death? >> i believe it was approximately $250,000. >> reporter: bill had other insurance payouts too. one when his automotive shop burned down, another on an investment property fire. he was also the beneficiary on policies for diane totalling $750,000. >> are you a guy that plays fraud games on insurance on the companies of bill? >> no. every one of those was investigated. >> is this all consistent, the arson, the insurance payouts, including up to diane's death? >> right. >> 'cause that's the picture that comes together against you. >> yeah. i understand that. >> this is not fraud on your part. >> absolutely not. >> reporter: but kevin, bill's main accuser, says the motive for his mother's murder is obvious. she was worth more dead than alive to his step-dad. >> let me hear your indictment for bill kyne for murder.

kills your mother why? >> money. $750,000 could help him out a lot. >> reporter: detectives thought they had a plausible motive. now they combed through bill's 911 call and his lengthy interview on the day of the murder. not everything seemed to add up. reporter curtis krueger noticed something curious reported by the first deputy at the scene. >> the first responders arrived, and attempted to take a pulse of diane, and they found her body to be somewhat cold. and that of course indicates that she may have been dead for a while. >> reporter: that deputy arrived just minutes after bill said he'd caught kevin in the act. diane's body temperature may have suggested a different timeline. detective beining was troubled by another part of bill's story. he said he never went back to check on diane after kevin ran off. >> i assumed that she was already dead. >> but it had all been so brief. did you get a good look at her -- >> no, i did not. >> what her condition was. i would think, when you come back in, you'd immediately go to her bedside and --

>> that's -- >> see what's goin' on. >> that probably would've been -- i wish i would have. >> but you didn't do that. >> i didn't do that. >> reporter: bill would not have had to check on diane if, as kevin said, he was the one who killed her. and when the crime lab reported on the first items sent for dna testing, the results seemed to place bill directly at the crime scene. remember, diane died of asphyxiation. testing showed bill's dna profile on a sample taken from her neck. >> we were a very loving couple. we slept in the same bed together. yeah, my -- my dna should be on her. >> reporter: a reasonable explanation for a bad fact. but was it the truth? detective beining reached into his toolbox for something to help assess bill's credibility. he asked him to take a lie detector test. >> you agreed to take a lie detector test. and you flunked the critical questions. >> i flunked certain questions. >> two questions, and i won't

paraphrase, but they both had to do with whether you caused her death or new what happened to her. >> reporter: one of the questions, "did you cause the death of diane kyne?" bill's answer, "no." another question: "did you lie about kevin being on top of diane on august 15, 2010?" bill's answer? once again, "no." according to the test results, both of those answers showed deception. >> central stuff, not peripheral stuff, the central questions. many you're not getting through the lie detector. did you lie? >> i did not lie. that's why they don't use lie detectors in courtrooms, 'cause they can issue false readings. >> if the guy's flunking the test and the son says he did it, it's not a good set of facts. >> no. >> for bill, is it? >> no. that's why we, now we have to attack bill. >> reporter: did they ever. beining, along with detective anthony stevens, brought bill in for more questioning the same day he flunked his polygraph test. this time they put the screws to him. >> she's dead and there's only two people who could have done it. okay?

and i'm here to tell you right now his dna's not on her neck and yours is. >> you also said you didn't go in the room, too. you already knew she was dead. that's why you didn't go in the room and the only way you could have known that is to possibly be involved. >> reporter: it was a withering interrogation and bill kyne cracked. he changed his story and said he did, in fact, go into his bedroom after the fight with kevin. >> why would you lie to us about certain statements? >> got no logical explanation. >> detectives don't like to be lied to and here he's told you a lie. first statement, i'm not in the room. now you're sweating him -- >> and -- >> -- and he is in the room. >> and now he's in the room. and it's like, you know, "bill, you said you weren't in the room. what's goin' on?" >> does he backpedal again from that story, detective? >> he does. he just says he's -- "i thought it would be better if i said i was in the room. >> reporter: if bill thought changing his story about going into the bedroom to check on diane made him look better, he was probably the only one. >> i have told you what really happened. >> which version are we supposed to believe?

>> you haven't been truthful to us at this point. >> you see how this is going? >> uh-huh. >> you fail a polygraph. your dna is on her neck. his isn't. >> the mountain's starting to build. >> reporter: detectives thought it looked like a mountain of evidence against bill kyne. what would the evidence say about kevin? >> reporter: coming up -- >> his glasses were found at the bottom of the bed. >> reporter: could there be a mountain of evidence against kevin too? >> i said your blood was found on your mom's leg. what's your explanation for that? [ male announcer ] you wouldn't ignore signs of damage in your home. are you sure you're not ignoring them in your body? even if you're treating your crohn's disease or ulcerative colitis an occasional flare may be a sign of damaging inflammation. and if you ignore the signs, the more debilitating your symptoms could become. learn more about the role damaging inflammation may be playing in your symptoms with the expert advice tool at crohnsandcolitis.com. and then

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>> reporter: detectives thought they had compelling evidence against bill kyne. and when they started checking out his stepson, kevin, they realized he'd been on their radar before. >> your deputies had a history of being called out to that house. >> they did. >> reporter: five years earlier, when kevin was 18, he got into an argument with his mother's sister. assistant state attorney bill loughery describes what kevin did next. >> the police showed up -- he fought with the police and -- even was trying to have his dog attack the police during it, so he was arrested for battery on a law enforcement officer and resisting arrest.

>> reporter: kevin pleaded guilty. and now, deputies from pinellas county were back at the house, this time investigating the murder of diane kyne. bill, who'd said his son did it, was painting a picture of kevin's violent past. >> i had never seen anybody act the way that kevin acted out. >> reporter: just three months before, bill said kevin had brandished a knife against his mother. >> he was frustrated about something and said, "you're going to listen to me." he had a knife in his hand. and it scared the heck out of her. >> reporter: kevin says that never happened. another time, kevin's mother bolted her bedroom door to keep him out. >> he kept pounding on the door and pounding on the door and he finally kicked it in. and it broke the door. >> reporter: was bill deflecting attention away from himself? or telling the truth about the man he insisted killed his wife? his daughter, rebecca, backed him up and attacked kevin in her interview with the cops. >> he was a little hothead. he would come in and throw his weight around.

>> reporter: like the time, she said, kevin tried to goad bill into a fight at the house, siccing the cops on him. >> he would puff up and get in my dad's face screaming for him to hit him, "please hit me. i'll call the police, and you'll go to jail right now." >> it was the classic kinda boy crying wolf scenario, because bill apparently hadn't done anything. it was just kevin trying to get bill in trouble and calling 911. >> reporter: kevin says he didn't goad bill, and made that call because bill shoved him. and things got so bad bill and diane even took legal action to throw him out. >> diane told him, "kevin, don't push me. you're going to see what we can do to get you out of this house." he didn't believe her. i went to my attorney. he drew up the papers and we had him legally evicted. >> you can do that? you can evict a child? >> he was 21 at the time. >> reporter: but diane loved her only child and couldn't cut the

cord. she let him come home. the summer of 2010, however, was racing towards a showdown. tensions in the family were high. the kyne house was cramped with four extra people. bill's son and his family camping out on couches because of financial troubles. kevin wasn't making things any easier, obnoxious about sharing the household computer. >> he was the computer hog. >> that's all he ever wanted to do was sit on the computer. it wasn't even his computer, but he would change the passwords and kick everybody off. >> reporter: kevin's mother was furious. she'd stop talking directly to him, trying to avoid the persistent arguments. >> they're just talking via e-mails? >> completely. >> 30 feet across the house and they're communicating by e-mail? >> not even 30 feet at times. >> reporter: the last straw was kevin cursing out his mother in front of the encamped family. >> called her a bitch, called her the "c" word. called her a retard. >> reporter: diane and bill gave kevin a deadline to get out for good, september 21st.

but five weeks before that deadline day, diane was dead, and bill said kevin's temper and violent past pointed to him as the only one who could have done it. >> did kevin kyne kill his mother, diane? >> yes. >> and the reason he did it? >> because he was being kicked out of the house and wanted to get his own way. >> and the reason that you should not be looked at for her murder is what? >> i didn't do it. i'm the one that pulled her murderer off of her that day. >> reporter: but kevin had already told detectives that that was all lies. he hadn't been near his mother. never made it into the bedroom. detectives, however, knew they'd found something important inside and it belonged to kevin. >> his glasses were found at the bottom of the bed. >> which seems to belie his statement that he didn't get into the room? >> right. >> reporter: kevin's violent history and those glasses did him in. he was arrested, charged with killing his mother and held in jail. but that wasn't the end of the story. not by a long shot. remember, bill kyne had flunked his lie detector test. kevin, meanwhile, had also agreed to be wired up.

>> they asked you the critical questions. >> oh, of course. >> all around one question, did you kill your mother? >> exactly. >> you passed the polygraph test. >> yes, sir. passed it, flying colors. >> when the polygraph stuff came back, your thought was, "we may have the wrong guy in jail here." >> reporter: the prosecutor acted quickly. he handed kevin a get-out-of-jail-free card, releasing this accused killer back into the community. >> i felt as a prosecutor, and my goal here is justice, that i thought it would be wrong to have kevin sitting in jail with -- with the status of the case at that moment. now, that doesn't necessarily mean we had enough evidence to put bill in jail. >> reporter: so the prosecutor convened a grand jury in early 2011, hoping to sort things out. he asked kevin's lawyers about letting kevin testify. allison miller was one of his public defenders. >> we found him credible. we found him compelling. shoot, maybe we put him in front of a grand jury and they believe him and he never gets indicted. >> i wanted the story out there. i wanted the truth to be out there. and i felt like it would help me

if i could present myself to these people. >> reporter: kevin told his story to the grand jury. how he stood at the bedroom door, shocked by his mother's ghastly appearance, and then bill jumping him from behind. >> he goes into how he never went in the room. >> reporter: but kevin was at a big disadvantage. >> he at that point doesn't know about the blood evidence. >> reporter: three specks of blood had been found on diane's leg and more on her bed cover. lab analysis, just back, showed it was kevin's blood, but only the prosecutor knew that. >> i said, "you know, your blood was found on your mom's leg. what's your explanation for that?" "i have no explanation." >> reporter: in the battle of competing stories, the grand jury broke the tie. kevin kyne's gamble to testify had backfired. he was indicted on the spot for first degree murder. >> as he's leaving the courthouse from the grand jury, he's brought back in and arrested again. >> reporter: the case had been unpredictable from the start. it had rival 911 calls.

conflicting murder accounts. >> my son just killed my wife. >> reporter: now in the courtroom, there'd be even more surprises. >> reporter: coming up -- the sandal scandal. >> he actually says "i've never seen them before." >> but what did science find? >> his dna was on them. >> reporter: would a jury vote to convict kevin? or could it all swing right back to bill? >> it's just so fake! >> reporter: when dateline continues. [burke] like how you thought you were covered for this... [man] it's a profound statement. [burke] but you're not even covered for this... [man] it's a profound statement. [burke] or how you may be covered for this... [burke] but not for something like this... [burke] talk to farmers and see what gaps could be hiding in your coverage. [sfx: yeti noise] ♪ we are farmers bum - pa - dum bum - bum - bum - bum ♪ all these networks keep making different claims. it gets confusing.

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>> reporter: july 2012. two years after diane kyne was murdered in her own bed, her son, kevin, stood trial for killing her. bill kyne, the other man who'd been under intense suspicion, came to the courthouse every day, his wife.

>> she was everything i'd ever dreamed of in a lady. we were going to spend the rest of our lives together. >> sheriff's office. >> reporter: in this unusual case of dueling 911 calls and conflicting murder accounts, the prosecutor was confident that blood evidence would sink the son's story and fully support the husband's. >> who was your best witness? >> i think probably anna cox was, really. >> reporter: anna cox, a blood-stain expert, testified that kevin's blood was not only on his mother but also on her bed cover. >> if he says he wasn't in the room, does your scientific finding deny that premise? >> yes. >> there's no question in your mind. science tells you he was in that room. >> yes. you had to be right next to the comforter. >> reporter: to the prosecutor, it was a home run, confirming bill kyne's story -- that he opened the door and saw kevin straddling the bed on top of diane. and, loughery argued, kevin's blood at the crime scene had to get there during a struggle with his mother or when bill pulled him off her. >> it put the lie to his story that he was not in there. >> there's no innocent

explanation. >> reporter: and his broken glasses had been found in the bedroom, along with birkenstock sandals, one inside the room, one by the door. >> he was adamant they were not his sandals. >> yes. >> he never wore them. >> he actually says, "i've never seen them before." >> but what did science find? >> his dna was on 'em. so, why would he lie about those shoes? and the reason he'd lie is 'cause the shoes show he's in the room. >> reporter: bill kyne took the stand to tell his horror story about that day. and he put his personal stamp on those birkenstocks. >> diane and i bought them for him or so prior to this incident. >> reporter: bill recalled the time when kevin tried to pick a fight with him, then called 911. testimony the defense fought to keep out but lost. >> i wanted the jury to know that he was like a boy who cried wolf who would make 911 calls frequently. >> reporter: bill said kevin was hardest on his mother, especially in the summer

of 2010 when she gave him the deadline to move out, and he cursed her out in front of the whole family. >> "that's it." she says, "i can't live with you one second longer." >> how close is that to the day -- the awful day? >> probably a week. >> reporter: the prosecutor theorized kevin just snapped and killed his mother in a rage after one last argument. >> kevin's lied. his dna's in the room. it's consistent with bill's story. it's inconsistent with his story. therefore, he did it. >> we both believed bill kyne was the person who killed diane kyne. >> reporter: the defense argued that bill's story was not true and that his dna was all over the crime scene. >> the dna on diane's neck, the dna on the pillows, the dna on the folded sheets, to me, was a sl that's reasonable doubt. >> reporter: the defense offered a theory that kevin's blood had sprayed toward the bed after he was scratched by bill in their fight at the door. the defense also argued that

bill was the real killer. >> if it's not our guy, it has to be him? >> we did say that. i don't know if it was just not as aggressively as it needed to be said. >> reporter: maybe if they'd hit bill harder, jurors would have found reasonable doubt. but they didn't. after four hours, the jury came back with a verdict -- guilty. second degree murder. kevin kyne was sentenced to life in prison. >> my throat went down to my ankles. i mean, it was a horrible feeling. >> there were no winners. kevin was going to be in jail for the rest of his life. i -- i lost the woman i was going to grow old with. >> it was heartbreaking. >> reporter: but allison miller still believed in kevin and wouldn't give up. murder convictions rarely get overturned but allison thought an appeal had a solid chance. she'd objected to the judge letting in the old 911 call kevin made to get bill in trouble. >> i argued that should not be admissible. >> reporter: she said it prejudiced the jury against kevin and an appeals court

agreed. two years after his conviction, kevin was granted a new trial. it was a stunning turnabout. allison rushed to phone kevin in prison. >> so, i called and said, "can i speak to kevin kyne?" and some very helpful person was like, "well, honey, it doesn't work like that. we can't just put him on the phone, you know? you have to schedule an appointment." and i was like, "can you just tell him he's getting a new trial?" >> i was astounded. i was extremely happy. >> i was hurting for my dad. no one on our side of the family had any doubt as to what happened that day. >> reporter: in february of this year, it was florida vs. kevin kyne round two. same courtroom, same judge and same prosecution strategy. >> there's really nothing to change. and, considering that he was convicted the first time, you know, it wasn't like you would say, "oh, we should have done it this way or done it that way." >> reporter: not so for the defense.

allison miller and co-counsel jessica manuele were in attack mode from the opening gavel. >> we're going to fight everything that needs to be fought. if we're going down, we are going down swinging this time. >> you know, the judge and the state, they kept telling' us, "well, this wasn't an issue the first trial." nobody objected to this the first trial. "hey, guys. i don't know if you realize but we're hoping for a different outcome." >> reporter: one jaw-dropping difference -- the defendant himself, a classic before-and-after weight loss, about 75 pounds worth. >> when i went to prison, my main goal was to lose everything and become fit. >> a lot of courtroom observers thought you cleaned your client up quite a bit. in appearances and also his interior, his demeanor, huh? >> yeah, he looked a lot more presentable and also he -- he grew up a lot. >> reporter: the defense had pulled its punches on bill kyne in trial one but not this time. >> he's the obvious suspect. >> reporter: now, it seemed as though bill was the one on trial. >> bill kyne has lied over and over and over again. he's lied to save his own skin.

he's lied to protect himself. he's lied to set up my client for murder. and the state expects you to convict kevin based on that man's word. >> it was funny. judge probably said 20 times, you know, "there are two sets of prosecutors in this room." >> reporter: allison miller played bill's 911 call, asking the jury to use its common sense. why didn't he rush in to save diane? >> sheriff's office. >> my son choked my wife. >> your son choked your wife? >> yes. >> okay. >> they were fighting and -- >> okay. hold on for me. >> it's so fake. i mean, the heavy breathing, and then he starts to get emotional. "oh, diane." >> oh, no, diane. >> it's just so fake. >> this case is about money. >> reporter: the defense also hammered hard on motive -- bill's. >> bill kyne collected $750,000 when diane kyne died. >> three quarters of a million dollars sounds a lot more like motivation to me than a computer password or wanting to stay in the house. >> reporter: the rebooted defense now had one last change -- a blockbuster new

witness. >> and what is your decision? >> i'm going to testify, ma'am. >> reporter: coming up -- on the stand, there'd be some changes, too. the sandals he never wore? >> no, i wore them. >> reporter: the bedroom he never entered? >> i might've took one or two steps just opening the door. >> reporter: will a jury believe his story this time? wish your skin could bounce back as quickly as it used to? introducing neutrogena hydro boost water gel. instantly quenches skin to keep it supple and hydrated day after day. formulated with hydrating hyaluronic acid which retains up to 1000 times its weight in water. this refreshing water gel plumps skin cells with intense hydration and locks it in.

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>> we felt confident that he would be able to hold it together. >> but you never know, do you? >> you never know. exactly. >> i think we all know who you are. but tell us your first and last name for the record, please. >> kevin lee kyne. >> reporter: this wasn't kevin's first time under oath. he testified before the grand jury and that's when he got indicted. now here he was again, putting himself and his story on the line.

it was a high-stakes gamble. >> were you and your mom close? >> very close. >> reporter: kevin was instructed by his attorneys, allison miller and jessica manuele, to talk directly to the jurors. >> we said if you expect them to believe what you're saying, you better look them in the eye and tell them the truth. >> did you ever call your mom a bitch? >> i did. >> did you ever call your mom a retard? >> unfortunately, i did. >> we said, "kevin, is this true? are you disrespectful?" "yes, ma'am." "well then, you concede it all." >> reporter: a pre-emptive strike, part of the plan to soften kevin and give jurors reason to doubt that an immature, bratty 23-year-old could turn into a cold-blooded killer. >> what this jury wants to hear is you say you didn't kill your mother. >> kevin, did you kill your mom? >> no, ma'am. >> reporter: but evidence of kevin's blood on diane's thigh had always been the defense's toughest challenge. >> the state's theory is the blood got there once bill and kevin start struggling. >> reporter: but, from day one, kevin had maintained he never entered the room when he was

attacked by bill. now, he would give himself and his blood some wiggle room to get closer to his mother. >> when you opened the door, did you take any steps into the bedroom? >> i might've took one or two steps just opening the door. >> reporter: in cross-examination, the prosecutor challenged kevin as a flip-flopper. >> this taking one or two steps, this is the first time you've said that in four and a half years, right? >> i was always saying that i opened the door and that's as far as i went. >> you were always saying you never went in the bedroom, right? >> i did not go further than the door, sir. >> i think kevin was probably in a state of shock, and i'm not sure he entirely knows how far he got in that bedroom. >> reporter: kevin also shifted his story on those sandals. >> you don't recall wearing these? >> no, i wore them. they were comfortable shoes just to slide on around the house, to go out and smoke a cigarette. >> i don't think i understand. so they're like the house shoes or something? >> correct. >> reporter: after kevin left the stand, his attorneys could only hope their new strategy,

clean up kevin and dirty up bill, had worked as the jury got the case and began deliberations. >> your honor, the jury has indicated they've reached a verdict. >> reporter: it took six hours. >> would you hand the verdict form to the deputy, please. >> the little time it takes them to get that verdict form from the jury box up to the judge, to the clerk to read feels like eternity. >> in the state of florida vs. kevin lee kyne the charge of murder in the second degree, the defendant is found not guilty. >> reporter: not guilty. >> that was probably the best feeling i felt in ten years. >> you got your life back that day? >> i did. >> reporter: kevin's paternal grandmother, his biggest supporter, cried tears of joy. across the aisle, bill kyne muttered to himself. >> i was devastated. i couldn't believe it. sometimes, the bad guy wins. >> you reclaimed his life. you pulled him out of the abyss? >> yeah, yeah. >> good job. >> you, too. >> any lawyer that tells you

they never lost a case never tried any tough cases. >> reporter: prosecutor loughery was still certain he put the right defendant on trial twice. >> it doesn't mean he didn't kill his mother. it just means that a jury said he didn't. >> reporter: the jury foreman said the defense's strategy to put kevin on the stand worked. >> i just don't believe that the evidence points to kevin. >> reporter: not only was there reasonable doubt, this juror believed kevin's testimony over bill's, in part because kevin looked directly at him. >> did that make a difference to you, making eye contact, acknowledging your presence? >> yeah. 'cause the eyes tell something. bill didn't look at us once. >> reporter: the next day, the judge released kevin. >> good luck, mr. kyne. >> thank you, your honor. >> please don't come back. >> i won't. >> good. >> reporter: outside, kevin met his grandmother and then the local media. >> i'm innocent. there's got to be a guilty party. >> where's justice for your mother in all this? >> i'm hoping, coming. so that way, justice is served

for my mother. >> reporter: the fifth amendment prohibits double jeopardy so kevin can't face charges in this case again. but bill could. >> i would like the prosecutor to ask the sheriff's office to reinvestigate diane kyne's death. >> that's silly. i'd love to be the defense attorney on that case. there's no way bill kyne would be convicted. because, not only does the evidence not show that, but the defense would be "kevin did it." >> who is kevin kyne? who is this guy? >> kevin kyne is a name on paper. that man is not a kyne. and he is not my family. >> so where's justice for diane in all this? >> kevin did serve some time in prison. and i -- i don't believe that diane would even want him to serve life in prison for her murder. but in my mind, he should still be behind bars. >> reporter: but now, kevin's got a second chance at life. he says he's dedicating it to his mother. >> she's looking down, and she sees that i'm maturing. and i am gonna be the man that she wanted me to be.

>> reporter: so, in the end, what do we make of this mind-boggling whodunnit where no one can say for sure who murdered diane kyne? leaving a husband and son, still pointing the finger at each other, still professing love for diane but one of them still defiantly lying about having killed her. >> reporter: that's all for this edition of "dateline." we'll see you again friday at 9:00/8:00 central. i'm lester holt. for all of us at nbc news, good

breaking news at 11:00. two teenagers shot in the street. the gunman drove away. tonight we're hearing from neighbors who went to the scene after shots were fired. >> and we just got this video in in the last hour. police looking for