Transcript for Murder-by-Family: When Loved Ones Hire a Hit Man
Hiring a hit man to make someone disappear. More than just a Hollywood plot line. It's a crime that's more common than you might imagine. The people you're about to meet thought murder might be the best way out of their relationship problems. Or at the very least an easy payday. One would-be killer allegedly wanted his own mother dead. Here's ABC's John donvan. Started as a joke. And it got out of hand. And it's cost him everything. Reporter: Big sky country. Land of open plains. But closed up inside this house, a family with a dark story. Everything changed in a matter of a few hours. Reporter: It begins on the outskirts of Billings four years ago at this used car lot when an FBI agent stops by to deliver to owner Dana Campbell an unthinkable message. He asked to speak to me in private. He said, I hate to be the one to inform you of this but we've been notified that there has been a contract put out on your life. A contract out for your life? It just sounds -- it sounds insane. Reporter: Not as insane as what comes next. The FBI agent says he has a pretty good idea of who took out the hit. It was her own son Matthew. They have enough evidence that they are safe in saying that it was my brother who had done that. He had contacted an undercover FBI agent and was making plans to have him kill my mom. Reporter: The big question, why? Nicky says she thought their family had an unbreakable bond. They enjoyed family trips together and only bickered the way Normal brothers and sisters do. We picked on each other and my little sister a lot. But end of the day we knew we had each other. Reporter: Matthew's family thinks he wanted something more. His mother's money. My two girls think now, maybe, if my estate had been divided into thirds after I passed away, maybe he might have even considered, you know, killing them so he could have 100% of it all. Made me question everything that I ever knew about him. You know. Was I next? Was my sister next? Reporter: We'll get back to that in a minute. Turns out trying to hire someone to make a loved one disappear may be more common than you think. Meet Julia marfeld who after pleasantries gets right down to it. In one of the most staggering conversations you may ever happen to overhear, she's planning her husband's murder. You said something about a gunshot, is that how you want me to do it, shoot him? Unless you can do it painlessly, I would -- I would prefer to use either a knife or a gun. Quick and easy. Less painful. Where do you want me to shoot him? Do you want an open casket, closed casket, what do you want? I want an open casket. Reporter: The stuff she's worried about, like the mess it might make -- In the house? It would be messy. Reporter: She didn't need to worry about because her husband is still alive. The guy she's talking to on the right hand, he is an undercover police officer. So why not just divorce her husband? Well, there was the insurance money to be had if they were dead. And then there were his feelings to consider. Divorcing him, I didn't want to worry about the judgment of my family, I didn't have to worry about breaking his heart, stuff like this, if I got a clean getaway. Reporter: Not so clean after all. She is now serving a sentence, at least five years and eight months. Hiring the wrong guy turns out to be a costly but not uncommon mistake. What they do is they step to a friend or associate or someone that they knew in their past. And what happens in the vast majority of the time, the person they step to goes to law enforcement. Really? They get ratted out? I'm 5,000% sure. Reporter: That's what happened to Delia Dippolito in 2009 allegedly negotiating terps for her husband's murder. Tours out the supposed killer for hire in the driver's seat was also an undercover top. Dippolito was called home by police and given the false news that inside her husband lay dead. Murdered. Okay, I'm sorry to tell you, ma'am, he's been killed. Oh, oh! He's been killed, man. No, no! Reporter: Then they got her into an interrogation room. I just want to see my husband. She continues to speak as a shocked widow. As far as she knows her husband is dead. Then they tell her the killer is one of their own men. That's an undercover police officer. We filmed everything that you did. Recorded everything that you did. I didn't do anything. Listen to me. I didn't do anything. You're going to jail. I didn't do anything, please, I didn't do anything. Reporter: Finally they tell her that her husband is still alive. Your husband is well and alive. Thank god. Oh, yes. Can I see him? He doesn't want to see you. Reporter: Delia's husband didn't believe her when she got him on the phone from jail. You know more than anybody it's not true. You sent me down to have me killed, I heard that. That is not true. How is that not true? How could you believe that? I heard your voice. Like I didn't do anything. It doesn't matter, you can hire 5,000 lawyers, they're charging your ass. They have your voice, your face, everything, on tape. Reporter: Dippolito was sentenced to 20 years. Just last week, an appeals court reversed that conviction because the jury was never asked how much they knew about her case. I didn't do anything and -- Reporter: Dippolito was granted a new trial. Through his lawyer Mike Dippolito says he's disappointed. People believe in their naive state that they can step to somebody else, have them commit the murder. They think if that guy pulls the trigger I'm clear. Reporter: Back in Montana, that's what it seems Matthew Campbell was counting on when someone talked to friend bss taking out a hit on his mother. But again, a problem. Somebody felt that my brother was seriously contemplating doing this. That person went to the department of corrections and basically told on my brother. Hey, Matthew Campbell wants to hire somebody to kill his mother. Reporter: That's all it took. An undercover FBI agent posing as a hit man approached Matthew. Matthew is busted and sentenced to five years in federal prison. On the outside, Dana and her daughters struggle to understand how this could have happened. Matthew tries to explain in letters home. This all blew up in my face. I can't handle it. I finally see where my lifestyle has gotten me. And I have been saved. In the name of Jesus Christ. All of this is cold, hard truth. And you don't have to believe it. But I hope you believe your son. Reporter: Over the last four years, letters like this kept coming. And with them, finally, a measure of forgiveness. The family now believes Matthew never really intended to kill his mother and they are waiting for him to come home from prison this month. He wants to move on and put everything past him. And we do too. I think, yeah, we're going to flourish into probably one of the best relationships I think I've ever had. Reporter: Hope springs eternal in big sky country. For "Nightline," I'm John donvan outside Billings, Montana.
This transcript has been automatically generated and may not be 100% accurate.