Transcript for Karl Karlsen's 2nd wife wears a wire to see if he will confess to killing son: Part 6
There's Karl. Collette getting the Turkey ready. Levi, boy, don't you look handsome today. This wasn't about a job. This was a passion. This was a passion to bring justice. Look at those two lovely people over there. For Christina, Levi and their My bride and joy sitting over in the rocker. Investigators in Seneca county get a tip, and that tip is look into Karl Karlsen. Look at that son-in-law of mine. That's when the tide starts to shift. Reporter: The year was 2012. It was about three years after Levi Karlsen had died, and as investigators begin to take a much closer look at this case, they learn Levi Karlsen had a life insurance policy and that his father Karl was the beneficiary to this $700,000 life insurance policy. That seems very odd when Levi had children of his own to leave money to. For me that was enough to re-open the investigation right there. It was the most terrifying time in my life. I decided that I just could not do it anymore. I couldn't live with Karl anymore. I needed to get out of the house. Shortly after I left is when law enforcement called me. First thing she said was, thank god you called. And then she said that she also had suspicions. They said they had a tip from a family member that maybe there was something more to Levi's death. That's when we started working together with law enforcement. Cindy was coming in on a regular basis. It was an ongoing process for months. I think she was almost kind of like -- almost wanting to be part of the police investigation team. I was watching a show where a woman was taping her mother, secretly, trying to get her to confess to killing her father. And I remember just thinking, I'm going to do that. I'm going to get a recorder and start recording my conversations with Karl. I met Karl in a busy restaurant. And Karl had actually picked the place, I think, because he was worried that I was recording. And I just told him that I'd consider getting back together with him if he came clean or confessed about every single thing he did during our marriage, every lie he told. You come clean, and I'll consider it. He actually confessed. When she came to my office, she was all excited, and she said, "He just told me he killed Levi." And she goes, and I recorded it. But what happened was it was inaudible. It was a poor recording at best and surely one that didn't capture all that Cindy thought it captured. Reporter: But now it's the detectives who have an idea, and they ask Cindy if she's willing to wear a wire to try to get Karl Karlsen to confess to this again. We're going to pick a rest want. We're going to put undercover officers in there for safety, and also to monitor. And we're gonna wire her up professionally and see if they can recreate this conversation. And I said yes. She's got the wire on where? Underneath her clothing. And what does he think he's He thinks he's coming to talk to his wife about getting back together. About reconciliation. But she has no plan to get back together. No. She's here for you. Yes. So the two of them are sitting together in the corner, and you had private investigators all throughout the room? Yes. Several of us sat in the immediate area with other investigators and plain clothes sitting inside the restaurant and nearby. Hi, two? Yep. Want to sit by the fireplace? Where would you like to sit? Over by the fireplace is good I think. Is that all right? Okay. Thank you. At this time now he's very suspicious that I want to hear the same things he did before. Did I purposefully do it? No, not at all. That's not what you told me, Yes, it is. No, it isn't. Part of me feels like I'm walking into a booby trap. He even said, "I feel like you're setting me up." How am I going to set a trap? Do you want to go through my purse? Karl's denying that he ever made any such admission, so we're kind of taken aback like, well what did he really tell Cindy? What's going on here? I couldn't get him to confess to the same exact thing that he had confessed two days before. You can hear Cindy Karlsen pressing her husband Karl over and over again. She doesn't give up. As the questions become more aggressive, Karl appears to make a halfway admission. I asked you if you pushed the truck, and you said yes. No, I didn't push the truck. I said. I said I had nothing to do, but I said I took advantage of a situation once it happened, and that is exactly what happened. Karl, you told me that you didn't set it up that way, but when you were in there you saw the opportunity. No, after it had happened. Then I panicked, saw the opportunity. Opportunity. A very strange word for a father to use about a son's death. I would find it very unusual that a parent would refer to the death of their child as an opportunity. For right now I need to -- I know, but I'm just telling you. -- Hear it. Did it fall hard? No. You just had to bump it? I mean, because it was so wobbly. You know? Because the only thing that was touching the ground is just the back two wheels. Any dessert? Oh, no. No, but I'll have more coffee, thanks. Sure. So then what happened? I mean, did he make a noise? It was instant? I thought. I mean, you'd think. It's not clear-cut and it's not definitive. By no means did we think this was a slam dunk. All right. I'll be in touch with you. Bye. Okay? All right, bye. At that point, we knew we we are going to be bringing him in for an interview. And they asked him to come in for questioning. They said, "Do you know what this is about?" And he said, "Oh, you want to talk about my dead wife and dead son." This isn't going to be a simple interview in a simple confession and we all know that going into this. Karl's very comfortable with them until they start asking him very pointed questions. That's when the interview turns into an interrogation. I didn't kill him. What killed him? The truck. How did the truck kill him? It landed on him. Just fell over. I felt like I was getting close. He was close to telling me what really happened that day. You're that close, man.
This transcript has been automatically generated and may not be 100% accurate.