Transcript for Man admits to stabbing, shooting doctor to death in alleged murder-for-hire: Part 4
Detective Zach Johnson has just gotten his biggest lead in the murder of Joseph Sonnier. That suspect's name is Dave Shepard, the divorced father of three, unemployed salesman with a criminal record. That was a name that detective Johnson had heard before when was talking to Mike Dixon's girlfriend, Ashley woolbert. He said that Dave was gonna come over 'cause he had some cigars for Dave from bermuda he was going to give him. He's just a common criminal. You know, I don't know how to put it any other way. David Shepard has a very long list of people that he's wronged over the years. David Shepard had been convicted of stealing $30,000 from a business that he was involved in. Dad didn't have money. Dad wasn't good at keeping money. I was 17 working part-time after school, and he borrowed money from me. As the police look into the background of Dave Shepard they quickly learn that his new best friend is Dr. Mike Dixon, the former boyfriend of Richelle. These two were an odd couple. I mean, you've got the down and out conman and the respected doctor. But they did have something in common. Shepard was going through a divorce. Dr. Dixon was going through a divorce. That relationship formed over the shared experience. This entire situation began, as police found out, when these two men, Mike Dixon and Dave Shepard, bonded over cigars and martinis. Dad wanted to be Mike. Buy the nice house that's right outside of town. In the canyon it's all private -- like, the whole nine yards. Mike had it all. And he would always promise us, "One day I'm gonna get you these things, and we're gonna live in the big house. And you're all gonna have your own rooms, and you get to paint it however you want. You get whatever you want." And he wanted that, and Mike had it. So he wanted to live the dream life of this wildly successful person, it sounds like, but was he willing to do the work to be that person? No. And Paul Reynolds had been living with Shepard for a few weeks. So he gives police insights into who this guy is as well. Personally I think he's just got super low self-esteem. I think he's just out there trying to find anybody that will convince him that he's something. Detectives are beginning to believe that Mike Dixon found the perfect person to help him get back with Richelle. I'll be honest with you, I loved, loved, loved that woman. And if not get back with her, disrupt her new love life. Something happened between these two that made Dave think that he needed to avenge Mike. And, apparently, Dixon was not only going along with it, but he was going to pay him to do it. In the minds of investigators, Dixon, they think, is a puppet-master, and Shepard, the puppet. It's around this time that police learn that Dave Shepard recently had a financial windfall. Dad had money out of the blue, and he didn't ever have money. We asked, "How do you have money?" He said, "I'm doing some work for Mike, and he paid me early." With the hotline tip from Reynolds linking Shepard to Sonnier's murder, and with the recent evidence that Dixon made a payment to Shepard, Zach Johnson's investigation kicks into high gear. And so we move on to arrest warrants. Who do you bring in first? We went and we brought in David first. He goes, "I want my attorney." Dr. Dixon do you have anything you want to say? Dr. Dixon comes in, and of course, he's madder than a hornet. I mean, I'm under arrest at 2:15 in the morning. You're under arrest, correct. This is probably your only opportunity to tell me what happened. I want an attorney then. Shepard and Dixon are both arrested and each is held on a $10 million bond. Neither one of them talks until the investigators offer Shepard a deal. For three months he stays silent. Finally they say to Shepard, "If you confess to this murder and you do it on tape, we will in turn take the death penalty off the table." It was real important for us and the Sonnier family to figure out what happened. And so it answered a lot of questions for a lot of people. What do you want me to call you? Dave? David? That'd be fine, sir. What he tells us is pretty chilling because it's very cold. This whole thing was like this stair step. We knew where it stopped, it stopped with the murder, but it had been building for months. Tell me about y'all's relationship, how it evolved. Two or three years ago, we were at a smoke shop. He's quick-witted. I'm kind of sassy smart and we just kinda hit it off. Smoking cigars is a very sociable thing. And we just connected and hooked up. When was the first time that he ever mentioned to you this Richelle shetina? My best estimate is September, October. She's around 49, 50 years old, smoking hot, looks younger than she was, thought she was great. He pretty much wanted to break up Dr. Sonnier and Richelle. They had this book. Yes. The complete book of dirty tricks. That they were trying to execute on, on Dr. Sonnier. What were some of the things they came up with? They were gonna get this porn subscription, like child, gay porn. And they were gonna send it to Dr. Sonnier's office. I gave him one suggestion to 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, his professional reputation. He asked me if I knew of a girl in Lubbock that would mind -- wouldn't mind making a thousand dollars to cause a problem. He was asking me if I knew somebody that would pretend to be, like, a sugar baby of Dr. Sonnier. I think Mike would have been embarrassed to tell me he was doing that. Because he knows I would've told him quit being a dummy. You know, this is ridiculous. You're -- why are you wasting this time? He said, "We have to follow him." He goes, "Let's take a little trip to Lubbock." We drove down to Lubbock. He was already trying to tell me where they go and that kinda stuff. Pretty soon Dave Shepard is taking trips to Lubbock on his own. Well they think that's at the direction of Mike Dixon. And he paid for everything -- paid for my gas, paid for my meals. And so when you went to his house, tell me about getting out and actually going back there to do the recon. Don't know exactly the first time I'd done it. Entered the backyard. Opened the gate. Took a picture. Closed the gate and left. It looked like a camera flash. And we kind of shrugged our shoulders and said, "That was weird." Did you ever ask Michael Dixon, "What are we doing? What's the next course of action?" We were at a club in somebody volunteered, they said, "Hit him with a board." I said, "You could probably kill him." Doc went like that. "We'll talk about that later." So they're having drinks one night. And so far, it's been nothing more than casual pranks. But they're talking about what comes next. You've got to out do what you did the last time.
This transcript has been automatically generated and may not be 100% accurate.