"20/20" continues. Here again, Jim mavila. Breaking news out of Gaston county. Reporter: It is breaking news. A shocking development in Gaston county, North Carolina's biggest murder mystery in years.... See More
"20/20" continues. Here again, Jim mavila. Breaking news out of Gaston county. Reporter: It is breaking news. A shocking development in Gaston county, North Carolina's biggest murder mystery in years. New developments in the Lucy Johnson murder case. Reporter: The man Lucy Johnson was in a bit earl custody battle is W is ruled out as her killer. And now in an even more surprising move, the man Lucy had told everyone was the answer to her prayers, Mike mead, is arrested. Police say Mike mead shot Lucy Johnson to death in her home last summer. Reporter: It catches everyone offguard, especially Mike mead, the successful local businessman, never before akulgzed of a violent crime. The man no one suspected of threatening Lucy is now charged with arson, rape and murder. Local TV reporter ken lemon was on the case from the beginning. When the charges came out, they seemed to come out of left field. Reporter: Prosecutors, motivated by the sympathetic, innocent victim, and the death of her unborn child, seek the death penalty. How did Mike mead become the prime suspect? Police became suspicious when they first brought him in. He denied killing Lucy but after this interrogation obtained by discovery channel, investigators are convinced that the whirlwind storybook romance is a sham. I felt so in love with her, so close to her. You know, it just hurts me thinking that you guys would even think that I -- Well -- I would have no motive. Why -- we were supposed to be on vacation this week, man. I was really looking forward to spending my life with this chick. But he usually described her in pronouns such as "Chick" or "That chick" or something to that effect. Which was very unusual. Reporter: Eddie Meeks is one of the prosecutors convinced mead is the killer. We knew he didn't trust her. And that was in direct contradiction to his "Love of my life" story. Reporter: And police say mead was suspicious and jealous, pointing to this exchange. When you were suspicious of Lucy a little bit -- Yeah, I just -- When she would have been -- Wanted to make sure she wasn't somebody else there banging her on something -- And she was banging somebody, what would you do? I'd walk out. Reporter: It was a tense few hours for mead. You are the one who is not telling us anything. I tell you what, man. This conversation's over. Okay? I'm done with this . I had nothing to Do with this. He seemed to enjoy the -- the cat-and-mouse game so to speak. Reporter: In fact, for police, Mike mead was his own worst enemy. They interview Lucy's best friend Deana Bradshaw who tells them about an odd conversation she had with mead the day after the murder. He was in too good of a mood. He was laughing. He was happy. He is talking about Lucy's breasts, and how he was going to miss them. He was not sad that he just lost his fiance. Reporter: Mead's behavior is enough to raise suspicion with Lucy's family. At Lucy's memorial service, her uncle says mead made more inappropriate comments. This time, about a 17-year-old relative. Mike leaned over and said, "Man, I'd sure like to have me some of that." This was at Lucy's -- Reporter: At the funeral? At her memorial service. The love of his life, as he called her. He was acting like he was at a party. Reporter: As prosecutors ready for trial, they work to build a case that Mike mead has a history of rough encounters with women he has dated. More than a dozen women who say Mike was vindictive, aggressive, pushy and outright creepy. You start to hear things like he has a pattern. A pattern of meeting women online. A pattern of relationship that seems strong and then all of a sudden it turns really bad. Reporter: A key witness for the prosecution, best friend Deana Bradshaw, says Mike and Lucy fought constantly about her pregnancy. Mike, she says, wanted her to get an abortion. He never believed that the baby was his. Her feelings were hurt. That he did not want her to have the baby. Reporter: Odd behavior, a possible pattern of aggressive encounters with women, and some circumstantial evidence. Would it be enough? It's off to trial in Charlotte, North Carolina. This is about cold blooded premeditated murder. Reporter: The prosecution tells the jury Mike is on a mission to be done with Lucy and the baby, and he wants his ring back. This was a $12,000 to $15,000 ring that Mr. Mead admittedly gave her. She's not the first person to have that ring but she definitely was the last. Reporter: If it was going to end, he was going to take the diamond with him. Reporter: Police never find that diamond but they were excited about another find at the house. The gold standard of evidence, DNA. The fire at Lucy's house did not burn everything. Evidence technicians are able to recover DNA inside Lucy. Diane Turbyfill covered the trial for "The Gaston gazette." There was some biological evidence of -- that Michael mead had had sex with Lucy Johnson within about 24 hours of her death. Reporter: Why does that matter? Prosecutors say mead denied having sex with her that night but police say he did and DNA proves it. What's more, they say it was rape. Lucy would not have had sex with him willingly. Lucy was pregnant and she had a condition that made having sex dangerous for the health of the baby. Reporter: It was a flashpoint in Mike mead's police interrogation. He is vehement the sex was consensual and several days before the murder. But you said you had sex with her after that. Really, because she begged and -- You still had sex. I don't know. Come on. No, but -- it was super gentle. Don't give us a bunch of crap that you didn't do this when you clearly did. Reporter: At trial, prosecutors aren't finished. They have a blockbuster surprise. A star witness who tells jurors, "Hold on." Mike mead, he says, confessed to him. That's right. Outright admitted he pulled the trigger that killed Lucy Johnson. Lucy's uncle can barely believe his years. He said that Mike mead told him that he didn't mean to shoot her the first time. That he just shot at her to scare her and it hit her. And it freaked him out so bad because she was jerking around and that he went and shot her again in the back of the head. Reporter: The prosecution ran with that. She reached out to him and said, "Oh, my god. You shot me. Mike, please don't let me die." Reporter: Powerful, huh? But there is a problem. That star witness, he has a bit of a credibility issue. You see, he is a convicted child rapist who says mead told him all this while both were locked up together for a short time in county jail. I've never confessed to a cop. I've never confessed to my lawyers. I've never confessed to anybody because I'm not going to confess to something I didn't do. But I'm going to confide in a guy who raped a girl. Reporter: As the prosecution closes its case, is the deck stacked against Mike mead, or is it a house of cards?
This transcript has been automatically generated and may not be 100% accurate.