and follow us on twitter. that is our program i had always wanted since i was a little kid, i'd see these older couples dancing. every step was perfect. and every move was in unison. they were one. >> reporter: richelle shetina was looking for the perfect partner in dance and in life. and she thought she'd found him in a wealthy doctor. >> he was a wonderful dancer and he introduced himself to me, "my name's joseph." >> reporter: but somebody else wanted to cut in, this plastic surgeon. >> hello, i'm dr. mike dixon. >> 911, what's the emergency? >> reporter: three people, trapped in what would become a dance of death. >> there's a bullet. i need somebody to hurry! >> there are police cars everywhere. there's crime scene tape all around.

>> it was an in-and-out job. a hit, to kill this person specifically. >> reporter: tonight, only on "20/20," the woman caught in the middle between two doctors. >> the kind of plot you'd expect from a soap opera. >> this is the oldest story in the book. this is vengeance. this is revenge. this is pride. >> reporter: a dangerous game of cat and mouse. >> accused of hiring a hit man -- >> there was some kind of triangle things going on. >> reporter: but who's the cat? >> no part of this is right! >> reporter: who's the mouse? >> this is a huge whodunit. >> reporter: a case with no shortage of suspects. a list of ex-girlfriends, a peeping tom in the backyard and a con man with his own obsession. >> i'm kind of a sassy smart [ bleep ]. >> reporter: he had a big man crush on mike. >> reporter: and tonight, with something he never said on the stand. he's talking only to "20/20."

>> reporter: characters so villainous, even their own children turn on them. >> you've made yourself a monster, dad! >> there are real sociopaths. sometimes they sleep in your bed with you. >> okay, game on. >> reporter: a last dance in texas. >> good evening. i'm elizabeth vargas. >> and i'm david muir. right here tonight, an all-new interview with a convicted killer, speaking only to "20/20." and telling us the opposite of what he >> it's gearing up for an appeal, the story of a couple taking a second chance on love. and the plastic surgeon that didn't want that to happen. an unexpected love triangle, but now there's a fourth person trying to break into their dance, whatever it takes. here's ryan smith. >> reporter: on a lazy summer afternoon in lubbock, texas -- >> 911, what's the emergency? >> reporter: a break-in in this

>> somebody has broken a window in the back and the doctor did not show up for work today. >> reporter: prominent local physician, dr. joseph sonnier, is found murdered. a landscaper finds his body. >> oh, no! oh, god. >> reporter: zach johnson, a detective with the lubbock police, heads to the scene. >> this neighborhood had to be freaked out by this killing. >> they were. they were very scared. because this doesn't happen, especially to somebody that's so esteemed. >> reporter: upon entering sonnier's house, it's immediately clear to detective johnson that this isn't a robbery gone bad. there was artwork in the home. there were very expensive pieces of furniture. nothing was taken. it was an in-and-out job. >> reporter: in the dining area, johnson can see where the fatal blows were delivered. >> and that crime scene was very succinct. it wasn't spread out. you had the overturned chair, you had the glass on the floor

so you knew that he was shot right here. >> reporter: another clue stands out, a gatorade bottle lies on the floor near the shell casings from the bullets. police determine it's a crudely fashioned silencer. >> we were dealing with something that was a hit, you know, of sorts. that somebody had come to this house, and to kill this person specifically. >> reporter: but who? >> to me, it was just mind-boggling. you know, why is this man dead? he's a well-respected citizen in this c >> reporter: sonnier's children are devastated and perplexed. two years earlier, their mother had been murdered, and now their father, too? for sonnier's oldest son, dallas, it's a hauntingly familiar scenario. >> i knew how to plan a funeral. i knew how to scrub blood off the floor. i knew everything we had to do, because i had already done it once before. >> reporter: this just doesn't happen. >> the statistical likelihood

murdered, separate occasions, is unfathomable. >> reporter: this all took place in lubbock, texas, nestled in the heart of ranching country, a broad and wind-swept terrain of cotton fields, cattle and money. >> you can't see better sunsets and sunrises and thunderstorms and everything else coming in. but, uh, it's the people that drive it. there's no better people probably anywhere in the world. >> reporter: one of those people is the victim, joseph sonnier, a well-known doctor, successful businessman and multimillionaire. and as far as women in lubbock are concerned, unquestionably a catch. he enjoys foreign travel, has a six-figure wine collection and even makes his own perfume. >> he was a single man in his late 40s with disposable income and an empty house. >> reporter: dallas remembers how his father fell apart when his mother walked out on him after 27 years of marriage for

>> she was the only person that he had ever been with and ever dated and ever fallen in love with. when they got divorced, it was a shock to him. everything he'd worked for in his life evaporated in one second. >> reporter: his ex-wife becky quickly remarried, and to the sonnier family's horror, she was murdered by her new husband, who then killed himself. james sonnier remembers how his father helped him and his brothers come to terms with their mother's murder. murdered and he became, like, our guide about how to handle this tragedy. >> reporter: and the elder sonnier was still in the process of rebuilding his own life. 48 years old and on the dating scene, dr. sonnier takes a chance. >> he went, i think, on a lark to a dance class, ballroom and salsa and swing.

he found his confidence again. >> reporter: and that's not all he finds. >> he started to meet beautiful single women, attractive women who were also, you know, in his age range. >> reporter: so that's how he was able to start dating again. >> and he got the mojo back like that. >> reporter: so how did you feel about the women that he dated? >> the truth is, we liked most of them. >> reporter: dallas and his brothers had grown up and moved away, but every fall they join their dad for a texas tech football game. one year, dr. sonnier brings a date to their family tailgate. >> she's blonde. she's tall. she's gorgeous. >> reporter: she is richelle shetina, single mother of four boys who sonnier meets at a ballroom dance class. >> it's a first date and he's bringing you around his family which is, that's nerve-wracking for some people. >> i mean, it was a first date. it really wasn't a big deal to me. i certainly wasn't nervous about it. >> she knew how to handle herself in a social situation

we're tough critics, you know? and we gave her a thumbs-up. >> reporter: like sonnier, richelle is divorced and has grown children. they begin dating, and when things start to get serious, he takes her to visit his grandchildren in los angeles. >> we had a great time. she came over to the house. we played with my kids. it couldn't have gone better. >> she's a smart girl, aren't you? >> reporter: while sonnier is enjoying dating richelle, dallas says, his father's feelings do not run to marriage. in your mind, he was never going to put a ring on it. >> that's right. >> reporter: but richelle may want more than casual dating. according to sonnier's family, she repeatedly tells him how much she wants to get married. >> it was constant pressure at every step of the way following the l.a. trip. >> that's not true. what i was looking for was a committed relationship with a good person. and that was it. >> reporter: a couple of months

richelle were going to paris. >> it was a birthday gift for my 50th birthday. i was just over the moon. it was really a dream come true. >> reporter: joseph and richelle's romantic getaway includes a trip to the pont des arts, a bridge across the seine river in paris famous for so-called love locks that line the bridge by the thousands. >> we bought a lock. and joseph wrote his name on it. and i wrote my name on it. and you throw the key into the seine river. and that locks in the moment forever. >> reporter: but for richelle and joseph, forever would only be a matter of weeks. on a sweltering wednesday in july, richelle learns that the love of her life has been murdered. >> there are police cars everywhere. there's crime scene tape all around joseph's house. you know, emergency vehicles there. there were reporters there. it was just absolute chaos.

chaos and confusion, detective zach johnson zeroed in on sonnier's girlfriend, richelle shetina. >> you always have to consider people the closest. because 90% of the time, it's going to be the people that are closest to our victims that commit the crime against them. >> reporter: the police take richelle in for questioning. she's on the hot seat and she starts naming names. >> there's just, you know, some girls that he dated. joseph would get these horrible text messages, you know? calling him a [ bleep ] and you know, "you're such a [ bleep ] and whatever." >> reporter: when

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"20/20" continues with a last dance in texas. >> reporter: joseph sonnier, a respected doctor, is found murdered in his home in an upscale lubbock neighborhood. and the first person homicide detective zach johnson wants to interview is richelle shetina -- sonnier's current girlfriend. he brings her in for questioning. >> how would you describe your relationship with dr. sonnier? >> he's -- he's the love of my life. >> meeting with richelle that very first time, i don't know a lot about her. there were a couple of things that were mentioned by her that struck me as odd. >> reporter: richelle tells detective johnson that in the months leading up to the murder,

watching her, following her to her gym. >> i had gone in to work out and i pulled into the parking lot and there was this big, creepy looking guy sitting there. and he was staring at the door like he was looking for someone or watching someone. >> reporter: she also thinks someone was hiding in sonnier's backyard, spying on the couple one evening after dance class. >> it was dark outside, and joseph and i both saw a flash from the outside. we laughed and kind of joked about, you know, maybe somebody was following us. >> reporter: detective johnson asks richelle if she knows anyone who might have stalked the doctor or held a grudge against him. >> joseph would get these horrible text messages, you know? calling him a [ bleep ]. and you know, "you're such a [ bleep ]," and whatever. >> reporter: and richelle has no shortage of theories about suspects. she rattles off a list of sonnier's ex-girlfriends. she also remembers a letter she received from a mysterious woman

>> and that she met joseph on the internet and that they had sex for money, basically. and, he said, "you know, this is obviously someone trying to drive a wedge in between us." >> reporter: police are intrigued by the idea of a love rival. but instead of focusing on sonnier's dating history, he asks richelle about her past lovers. one name is on the tip of her tongue. >> his name is dr. thomas michael dixon. he's a plastic surgeon in amarillo. >> reporter: dr. mike dixon. >> hello, i'm dr. mike dixon. if you're considering plastic surgery -- >> reporter: well known, he's divorced, wealthy, and used to date richelle. >> he had a med spa in amarillo. and i went there to get botox injections. >> reporter: what attracted you to him? >> he was funny. he was very witty. and he was enjoyable. you know, if it can be enjoyable to have somebody put needles in your face, you know, i guess that's about as enjoyable as it could be.

dr. dixon had dated for a year and a half before they broke up and she started seeing dr. sonnier. >> did he know about your current relationship? >> he knew that i was dating joseph. he called him by name in a series of text messages trying to get me to go out with him, to meet him for coffee. >> reporter: richelle says she rejected his advances, but he was persistent. >> so he wanted you to see him on the side, basically? >> he wanted me to come back to him. i told him, "no." >> reporter: but is dixon the kind of man to take "no" for an answer? johnson wants to find out. so he drives two hours to amarillo for a face-to-face conversation with richelle's ex -- that the detective secretly records. >> dr. dixon? i'm detective johnson with the lubbock police department. we've got a case down in lubbock, and i'm needing to talk

richelle's boyfriend." and his first thing was, "oh, well, i don't know anything about him." >> i don't know anything about him. i haven't talked to her in months and months. >> and i was like, okay, well, that's a little odd. because in our interview with richelle, she told us that he knew about the relationship. >> yeah i'll be honest with you. i loved, loved, loved that woman. i really did. >> he was obsessed with richelle. he was having a lot of problems getting over this break-up. he just couldn't seem to let her go. >> reporter: for detective zach johnson, alarm bells were sounding. >> i really had fallen head over heels. in fact, made a lot of life changes for her. >> he's very upfront about, "yeah, i wanted her back." >> reporter: dixon recalls how their relationship ended when he failed to propose to richelle on her birthday -- and instead gave her a subscription to a tea-of-the-month club. >> and she went ballistic, and said, "well, it isn't. it's not a big [ bleep ] rock." i said, "no, it's not." like a wedding ring. >> it wasn't about the fact that

i don't happen to drink it. he was not present in any emotionally supportive aspect of my world. >> reporter: but despite richelle's unhappiness with him, dixon says they kept in contact after their break-up. >> she was like, "hey, do you want to put this back together?" i was like, "yeah, i do." and so, let's plan a trip, blah, blah, blah. the next day, she's like, "hey, sorry, i'm in love with my dance partner." >> he still loves her. he's got a lot of feelings for her. but boom, she drops the hammer on him, and says, "oh, by the way, i'm in love with my dance partner." >> reporter: some would say, "well, you're throwing it in his face a little bit." >> well, no. i wasn't throwing it in his face. there was, you know, an ugliness from him to me. >> reporter: dixon seems like a likely suspect, but he has an alibi the night of sonnier's murder, as do richelle shetina and those ex-girlfriends. detective johnson is stumped. >> there's something not right here. this is a huge whodunit.

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>> reporter: homicide detective zach johnson is desperately trying to unravel a tangled web, but he has no viable suspects in the murder of dr. joseph sonnier. until he gets a phone call. what was it that broke this case wide open for you? >> when paul reynolds called the police department. >> my name is paul reynolds, and we -- we think we've got a crime that happened down here in lubbock. it's a homicide. >> who is paul reynolds? >> believe it or not, there are good people in the world. and paul reynolds is one of them. >> reporter: reynolds is a

named dave shepard offers to let him crash on his couch. he offers to tell police everything he knows. >> he kind of started in with just weird talk. >> reporter: according to reynolds, shepard starts acting strangely, telling wild, violent stories of killing a man in lubbock. incredulous, reynolds googles the information, only to discover that the murder is real. >> and then these stories started to come out. >> reporter: reynolds tells investigators that coincidentally, shepard is a good friend of none other than richelle's ex, dr. mike dixon. the investigation takes a turn, zeroing in on shepard. >> and tell me about y'all's relationship, how it evolved. >> he's quick-witted. i'm kind of a sassy smart [ bleep ]. >> reporter: shepard tells investigators he and dixon bonded over cigars and martinis at local hangouts in amarillo, commiserating over their ex-wives. >> smoking cigars is a very sociable thing. and we just connected and hooked

>> shepard's daughters, haley, abigail and rachel, speaking exclusively to "20/20" about the strange bond between their father and dr. mike dixon. >> dad was definitely obsessed with mike. like -- >> reporter: really? >> he had a big man crush on mike. >> reporter: it was an unlikely bromance. dixon, a successful plastic surgeon, and shepard, a divorced, unemployed conman. so what did your dad see in him? >> his money, and his success. >> dad wanted to be mike. >> reporter: shepard may have been obsessed with dixon, but dixon was obsessed with someone else, richelle shetina. >> he left his wife for her, you know, that she broke up his marriage and he just wanted, i guess, payback. >> david shepard does come in and tells us exactly what happened. >> reporter: so he tells you everything? >> this whole thing was like

a prank. >> reporter: shepard tells police that it all began harmlessly enough, trying to tarnish dr. sonnier's reputation in the hope that richelle would break up with him and run back to the arms of dixon. what were some of the things they came up with? >> they were going to get this porn subscription. >> go to an adult bookstore and buy the most obscene, nastiest, man-boy love association book he could and buy him a subscription and send it to his office. because i said, "that's a gift that'll keep giving." >> they were thinking that was going to ruin his reputation. >> reporter: as the months go by, and richelle is still dating sonnier, dixon becomes desperate. >> he said, "we have to follow him. we have to figure out where he's at." he goes, "hey, what are you doing? let's go. let's take a little trip to lubbock." >> reporter: they drive the 120-mile stretch of highway between amarillo and lubbock. >> and next thing i know, he tells me that richelle and

and he showed me where the dance class was, where to go. >> reporter: shepard spends months in lubbock, watching the lovers. turns out it was shepard who scares richelle in the early morning hours when he's staking out her gym. and it's shepard who, in a brazen move, breaks into sonnier's backyard and takes this accidental selfie, the flash alerting richelle and sonnier inside. >> it looked like a camera flash. and we kind of shrugged our shoulders and said, "that was weird." >> reporter: shepard fails to dig up dirt on sonnier. so dixon grows impatient. >> was there a specific act that he was wanting done that was that what y'all was discussing? >> yes. >> and what was that? >> he wanted him hurt. and then it gradually developed into having him killed. >> reporter: after hours of interrogation, an exhausted shepard gives police a blow-by-blow of what happened

july 10th, 2012, is the last night shepard will stalk his prey. he breaks into sonnier's backyard armed with a gun and a knife, and lies in wait. sonnier comes home, makes himself a drink after a long day at work. suddenly, shepard is at the back window. >> pulled the gun out of the bag with the gatorade on it. i point the weapon with the bottle at him. >> reporter: shepard pushes through the window and fires, emptying his gun into sonnier. the doctor somehow finds enough strength to stumble out of the room to get away. but shepard is in pursuit, and finds him in the garage where he stabs him 11 times. >> he's laying on the floor, not moving, not breathing, nothing. i check his pulse in his neck. he's dead. >> reporter: district attorney matt powell offers shepard a

dr. mike dixon, in exchange for a life sentence instead of a death sentence. >> he's a murderer. he's a liar, he's a thief, he's an embezzler, he's lots of things. as far as his role in this, i think he was a pawn for mike dixon. >> reporter: but who will the jury believe? a respected plastic surgeon or a convicted conman? when "20/20" returns. technology is useful.

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"20/20" continues with a last dance in texas. >> reporter: despite the fall chill rolling across the outer western plains, in downtown lubbock, things were heating up. as the biggest murder trial this town has ever witnessed kicked off. >> this prominent plastic surgeon, dr. michael dixon, accused of hiring a hit man, friend and business partner

>> i cannot believe that they did this. it makes me so angry. a lowlife scum and a piece of [ bleep ] doctor. >> reporter: dallas sonnier was hell-bent on bringing his father's suspected killers to justice. what was your mindset going into that first trial? >> let's go get these guys. >> reporter: the man tasked with putting mr. mike dixon away, a hard-charging texas district attorney named matt powell. >> mike dixon was running this show and he orchestrated this whole thing. >> reporter: but many people make the argument that mike dixon never laid a hand on dr. sonnier. >> he's just controlling the knife. dave shepard's just another instrument for mike dixon. >> reporter: and that instrument, dave shepard, has agreed to testify. pitted against his best friend mike dixon to avoid the death penalty. >> this is the oldest story in the book. this is vengeance. this is revenge. this is pride. >> reporter: the motive? in courtroom 72 of the lubbock county courthouse, the prosecution paints a picture for the jury of dixon as an

>> he either wanted her to suffer or he wanted her back. and only he knows what the true answer to that question is. but dr. sonnier was in the way. >> reporter: the pillars of powell's case, police find the gun shepard used at the bottom of a lake conveniently located behind dixon's office and discover it's registered to dixon's brother. and, they also find surveillance videos from the day after the murder. that's shepard in the plaid shirt, dixon in blue. the two hanging out, thick as thieves. but shepard is struggling with the knowledge that he killed a man. >> was there any discussion about when the police went over there and spoke to him? >> he was nervous. he said i had to get out of town. >> reporter: but he didn't, instead shepard attempts suicide. he slits his wrists. when he fails, who does he call for help? his buddy mike. here they are. that's shepard towering over dixon as they head into the doctor's office to stitch shepard up.

does he discuss anything with you in reference to sonnier? >> he told me to keep my cool. >> reporter: prosecutors also have a myriad of incriminating text messages between shepard and dixon, as shepard stalked sonnier for months. messages from dixon ordering shepard, "you have to stay close. watch him in the a.m." "go get them." and, "put it on them." finally, what's the price for murder, between friends? police say dixon paid shepard for the hit in the form of a box of cuban cigars and three silver bars. bars that turned up at this pawn shop in amarillo. one before the murder, two the day after the murder. sold by none other than dave shepard. in terms of demeanor he didn't strike you in one way or another, it sounds like? >> not at all. >> reporter: a couple days later, he is on the front page of the paper. >> i was blown away. >> reporter: but dixon's lawyers have an explanation for all of this. first, the gun used. they say shepard stole it from dixon's home. defense attorney frank sellers

>> they came in here and they're picking out cigar to smoke and shepard opens this drawer here and it's a gun. >> reporter: so that's how shepard knew a gun was in that drawer. >> exactly. >> reporter: and the silver bars? the defense says they were for a business investment, not a murder for hire. they say dixon only wanted shepard to try to take photographs of sonnier out with other women, to show richelle sonnier wasn't all he was cracked up to be. >> in days before they leave for paris, he says, "it's got to happen tomorrow, because the trip is imminent almost sounds like somebody's trying to say attack or hurt somebody imminently. >> we believe that it was an attempt to make the trip uncomfortable. get the photographs. >> reporter: and they say this was all because dixon was upset. he believed richelle was throwing her new relationship in his face. >> richelle was posting on facebook all the time how dr. sonnier was ten times the man that mike dixon would ever be.

that she was wrong. >> reporter: so from your perspective, it wasn't about richelle shetina, it was about mike dixon and his ego? >> right, if he was obsessed with her he'd of been following her. >> reporter: were you in any way trying to flaunt your relationship? >> he was blocked from my facebook page. so was i flaunting anything? no. >> reporter: dixon's attorneys say dave shepard simply went rogue when he killed sonnier. do you at least admit that he planted the seed by even discussing this relationship? >> planted the seed for a murder? no. absolutely not. >> mike is morally responsible for david shepard being down here. but for not the purpose of killing dr. sonnier. mike dixon never wanted that to happen. >> i asked him, "you sure you want to do this, mike?" i said, "if you were, when you kill somebody, that'll affect you for the rest of your life. you'll have nightmares.

and he goes, "doesn't bother me." >> reporter: and when it was time for the triggerman to testify against his best buddy in open court, the sonnier family was sitting front and center. >> he had a chance to get up there, confirm his story, point to that guy as the person who paid him to kill my dad, and end it all. >> reporter: but the bromance is still on. shepard is about to change his whole story to save mike dixon's skin. >> did mike dixon ever ask you to kill dr. joseph sonnier?

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>> reporter: when the confessed murderer david shepard took the stand at his best friend mike dixon's trial, he was facing the victim's family, the jury, but perhaps most poignantly, his three daughters -- rachel, abigail, and haley. and they are not here to defend their father.

get closure? >> we were there more in support of the sonnier family. >> right. >> yes. >> our heart was broken for them. >> reporter: shepard's daughters saying their father is a murderer. and do you think that mike dixon paid your father to kill dr. sonnier? >> yes. >> reporter: but on the stand, a shocking twist nobody saw coming. >> shepard himself has basically denied all his previous testimony. >> reporter: the man whose confession was expected to put mike dix letting his frien completely off the hook, while leaving a veteran prosecutor blindsided. you begin to question him. what happens? >> well, he completely digressed from what his statement was to law enforcement in the fact that mike dixon didn't have any involvement in this deal. >> reporter: what's going through your mind? >> "okay, game on." >> in that moment, i've never hated anyone more than i've hated him in my entire life. >> reporter: if shepard flip-flopped on the stand in hopes of freeing his friend, it works. the case ends in mistrial. >> the only reason for the hung

>> it was cowardly. >> he has a chance to make it right. and he completely ruined it. >> reporter: why do you think he did that? >> he was trying to help out his buddy. >> reporter: back in jail, his daughters confront him. it's a rare and raw look at a fractured family. >> but daddy, you didn't tell the truth. >> i did. >> you didn't say anything, you just kept saying that you wouldn't tell them. >> but i did. >> why didn't you tell -- no, you didn't, dad, you said, "i plead the fifth. i don't -- i'm not going to answer that." none of it will ever be right. >> there's nothing i could do. >> no matter what you do. >> they think i'm some kind of a monster. >> you've made yourself a monster, dad. >> reporter: i mean, and you were literally breaking down in tears. >> it was frustrating. i felt like i was scolding a child. like, i just want you to answer my question, and then you can go back to time out. >> reporter: shepard is now in a permanent time-out, a life sentence at this maximum security prison in west texas for the murder of dr. joseph sonnier.

flip-flop, he is sticking to what he said on the stand. your daughters told us that they were so upset that this was your chance to get up there and to tell the truth, and that in their mind you lied. >> yes. >> reporter: how does that make you feel? >> pretty bad. they know me. they should know when i'm telling the truth and when i'm not. and i was telling the truth on the stand. >> reporter: unlike the story shepard told police of a cold-blooded hit on sonnier -- >> i pulled the gun out of the bag with the gatorade on it. i point the weapon with the bottle at him. >> reporter: he says the truth is, neither he nor dixon ever intended for sonnier to die. it was all a tragic accident. did mike dixon ever ask you to kill dr. sonnier? >> no, absolutely not. absolutely not. >> reporter: but remember, he confessed to police that dixon wanted him to kill sonnier. >> he wanted him hurt. and then it gradually developed into having him killed.

interrogated you, you said that mike dixon was a part of this. >> right. >> why did you tell them that? >> i embellished. i felt that's what i had to do. >> reporter: shepard claims he told a tall tale to save his own life. so in your mind, you made up the story that mike dixon was involved to get the death penalty off the table. >> yeah. >> reporter: the real story, according to shepard, is that mike dixon wanted him to keep tabs on his ex-girlfriend richelle and her new boyfriend. so he asked shepard to follow them and take pictures. why'd you help him with this? >> seems kind of silly, looking i didn't want to offend anybody. i don't want to hurt anybody. and i sometimes have a hard time saying "no," i guess. >> reporter: there were all these text messages that mike dixon was sending to you "go get them," "whip and spur." so those text messages were referring to? >> i would assume, staying on target, so you can get a picture of him with another girl besides richelle. >> reporter: and on that muggy summer night in july, shepard and sonnier finally come face-to-face in sonnier's backyard and police say shepard is armed with that gun, the

so what happened that night? >> i'm in his backyard. he knocks on the window. and i waved, i waved at him. i said, "i'm showing you some stuff." he goes, "oh, all right." i lift stuff up, and then the world went -- things got out of hand. unintentionally, gun fired. i'm leaning in to see if he's okay, i fall in the window. and then, he's getting up, and going around. i'm running around to see what's going on, i said, "dr. sonnier, are you all right?" i don't hear anything go in the hear his last breath. i reach down, there's no pulse. >> reporter: in a bizarre and misguided attempt to cover up the accidental shooting, he plunges his knife into sonnier's lifeless body. did you stab him? >> i did stab him a couple of times. i can't reconcile the number that the prosecution says. 11. i think they've said i had dr. sonnier's phone in my hand and i considered dialing 911 just to call the authorities and i didn't.

mutilated his bodily remains, and tried to cover it and make it look like something else. >> reporter: do you consider yourself a cold-blooded killer? >> no, absolutely not. an idiot, you know? careless. i mean but, no. no. >> reporter: after the murder, shepard says he drove to dixon's house back in amarillo to tell him in person what had happened. >> i said, "mike, things didn't go like i hoped." he goes, "what are you talking about?" and then i broke the news to him. and he's like, "so you're telling me --" i said, "yeah." and he goes, "well, we'll just have to see what happens." >> reporter: less than 24 hours later, the police were at dr. mike dixon's door. dr. mike dixon's door. >> dr. dixon? i'm detective johnson with the lubbock police department. >> reporter: but why wouldn't he have shared all that with police who were then coming by his house? he didn't even mention your

didn't know what to do and he's like, okay. "let's not bring dave in 'cause then we're like throwing dave under the bus." plus it looks bad for him. i was trying to get pictures about this guy that was dating his former girlfriend. i didn't mean to kill dr. sonnier. i have nothing against dr. sonnier or his family, or richelle shetina. i have nothing against any of them. i really don't. >> reporter: what would you say to them right now if they were watching? >> i'd tell them that i'm very sorry. i took your loved one. >> reporter: despite shepard's second story, the prosecutor is undeterred. and a year after the mistrial, mike dixon faces a retrial. >> amarillo doctor michael dixon is back on trial -- >> reporter: and this time around, matt powell has a new witness. >> the number one most important thing from this second trial was the unbelievably courageous testimony of haley shepard. >> reporter: next -- dave shepard's own daughter haley takes the stand, and what she recalls about a simple steak

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there's nothing like trying something new. especially when it comes to snacking. that's why we're introducing cheese dippers. the creamy cheese and crunchy breadsticks cheese dippers by the laughing cow. reinvent snacking. >> reporter: lubbock, texas. haley shepard, the hitman's

she takes the jury back three years. and you'll see why. it's a hot summer night in amarillo, texas. her father, dave shepard, treats his daughters to a fancy steak dinner, served with a side of suspicion. >> he had some money. i got a nice steak. >> reporter: shepard's daughters say that night, their typically cash-poor father bragged about buying a new grill and new tires for his suv. >> dad had money out of the blue. he just randomly had money, and he didn't ever have money. >> reporter: for his older daughter haley, there was also a brand new cell phone. >> we all asked him, "how do you have money?" and his words were, "i did some work for mike, and he paid me early." >> reporter: this time, the prosecutor calls her, not her father, to testify in mike dixon's retrial. and you think that was a prepayment for killing dr. sonnier? >> in retrospect, absolutely. >> reporter: for victim

testimony is a game changer. >> she got up there and said, "at dinner, i asked my dad," i said, "where'd you get this money?" and david shepard says to her, "i did some work for mike. he paid me early. don't ask what i did for him." game over. >> reporter: it takes a new jury only three hours to deliberate. >> and my hand was shaking like this. because i knew we'd got a guilty verdict. i knew it. i knew it. i knew it. >> reporter: and he's right. >> the verdict is in. >> unanimous verdict. >> guilty on two charges. >> reporter: mike dixon is convicted on two counts of capital murder. what was your first reaction? >> i had to turn to my wife and i had to say, "he -- he said guilty, right? he said guilty?" we've been waiting for that moment for over three years. >> reporter: for the sonnier brothers, it's finally closure.

of him -- smug smile. when you look at his mug shot from his arrest -- smug smile. and he has had that smile for both trials. and it was so great to be able to know that we finally wiped that smile off his face. >> reporter: remarkably, dave shepard's daughters have accepted both men's fate as justice served. i know you guys don't talk to your dad a lot right now, but if you could, what would you say to >> we're doing very good. we are all okay. >> we're okay without him. >> i think he's where he needs to be. >> reporter: as for the woman at the center of it all, richelle shetina has a warning. >> there are real sociopaths and psychopaths that walk amongst us. they're charming. they sit at the dinner table with you and your children. and sometimes they sleep in your bed with you.

love for you or empathy for anyone. when you see that, don't ignore it. get out. run as fast as you can. >> both dave and his onetime best friend are now serving life in prisonithout the possibility of parole. dixon's lawyers are going to appeal the verdict. >> our question for you, how much of a role do you think dixon played in getting shepard to commit that killing? let us know, use #abc2020. i'm elizabeth vargas. >> and i'mright before the cras. plus ... [sot "911 emergency?"] contact 13's darcy spears listens in to 911 calls hijacked by bogus emergencies. and, look at this ... people walking near the strip

but we begin with breaking news. this disturbing image of a dog with duct tape around its mouth has animal control officers outside a valley house right now investigating. 13-action news is first on the scene near alexander and torrey pines. lets get out to bryan callahan with details on what we're hearing from police right now. bryan. metro is waiting for one of their animal cruelty detectives to arrive here on scene. this after animal control a call and found the dog with tape around it's mouth. an neighbor who wants to remain anonymous want us this photo of the dog. metro says animal control officers determined this could be a case of felony animal cruelty and called them to the scene. we are told the dog has worked the tape free from it's mouth,