He was on the verge of making it big in the music business and he seemed to have it all. To everyone else, the rapper known as g. Dep had a bright future. But he was haunted by his past, hiding a... See More
He was on the verge of making it big in the music business and he seemed to have it all. To everyone else, the rapper known as g. Dep had a bright future. But he was haunted by his past, hiding a terrible secret his conscience just wouldn't let him forget. So he made an incredible decision to take justice into his own hands. Here's abc's deborah roberts for our series "crime and punishment." ♪ this is a tale of music. Murder. And redemption. If you had it to do over again, knowing you'd go to jail for a long time, would you still confess? I would do it again. You know what I mean, because -- I don't there was no other way around it except me dying. His name is g. Dep, short for ghetto dependent. Sean combs even teamed up with him in his video. He paid a great debt for committing a crime, betrayed by the last person nip would have suspected -- himself. It was the only way I could have been absolved, you know, personal sacrifice. How he got there is a story in itself. G. Dep dropped out of college at 18 in search of a music career. He paid for recording sessions by selling cocaine on the streets of harlem, new york. He dabbled in drugs. In the fall of 1993, a month before his 19th birthday, he mugged a stranger with a gun. Standing under the scaffolding on park avenue, 114th street. I was riding my bike. I said, give me the money, man. The guy grabbed the gun, you know, I pulled the gun back. And that's when I fired. How many times did you fire? Three times. He fled on his bike. As he left home the next morning, police were canvassing the neighborhood. They said do you know anything about a shooting that occurred yesterday? I said no. That made me think he didn't pass away. A week later he got rid of the gun. I went to the east river and threw it away. That was the end of that? Yeah. ♪ coleman stayed quiet about the harlem shooting. Throwing himself into his music. Then five years later, he caught the eye of sean combs. How much were they going to pay you? Well, the record deal was for $350,000. You know? It was definitely, you know, more money than I have ever seen. He had a daughter with a girlfriend. That relationship ended. Then he met crystal sutton at a club, they married in 2004 and had twin boys, now 9. He has such a great heart. He's always so forgiving and caring. He had fame, fortune and now a family. And the stain on his past. How much did it eat at you? It seemed like it wasn't fair for me to, you know, be happy. You know what I'm saying? I used to curb my happiness. You know? Like just -- now, wait a minute, I'm smiling and laughing too much. He remained haunted by his secret, that shooting in harlem. What ever happened to that man? Was he dead? I thought about whether or not he had children because of being a father. Here I am trying to be a father. Did anybody know that you were hiding from this demon? This thing in your past? I feel like I couldn't really tell anybody because I didn't want them to be involved. Burdened by an unbearable secret, g. Dep's music suffered and combs dropped him from the label. It was probably the drugs. I was knee deep in trying to medicate myself. Everything was boiling down. The guilt? Yeah. To that. In late 2010, coleman couldn't bear it anymore. He confessed to a police officer he had shot a man 17 years before. The police did nothing. Maybe he thought that you were just faking this. Yeah. Incredibly, coleman later went back to police to confess again. What led you to walk into that police station? I think I was at a point where it was like enough is enough. But nobody else knew about it? You could have just kept quiet and dealt with it on your open. Dealing with it was killing me. Coleman's memory of the incident was vague. I didn't realize it was hitting him or anything, because I didn't -- I didn't see anything, you know? I just fired. But police soon found the cold case of john henkel shot in 2003 at park avenue and 114th street. And then after a while, you know, after I told them what happened, you know, he said -- i wanted to let you know that the guy died. Suddenly, you're charged in a murder. Did you start to have second thoughts? No. Trevell coleman had charged himself with murder. You have to concede that that man probably lived in a jail in his head for 18 years. Editor-in-chief of "gq" magazine he was the jury foreman. He didn't need to come forward but did. He needed to come forward for his conscience. But we were wrestling with it as jurors because this man has gone through hell. And he's done something noble. But he did kill someone. I completely understand that for the people who knew john henkel it's a different story. The jury found coleman guilty of second degree murder. On may 8, 2012, he was sentenced to 15 years to life in prison. The case of trevell coleman has haunted me. When your twin sons said shortly after you were arrested, he said I'll take money from someone and if I get arrested i can go to jail and be with daddy. That must have broken your heart. Yeah. So they understand that that dad chose to turn himself in? Yes. They're proud of him. I have one really tough one and then one that, yeah, he'll cry. Coleman had separated from his wife in 2008, but crystal says she's standing by him. He said to me that in some ways he feels freer now, even though he is locked up. It's a different trevell to me, not on drugs. He feels freer and that you can tell when talking to him. Do you think he made the right decision? Whatever decision trevell chooses to make and I have to stand by him. There are relatives of this victim who can't believe that you confessed. Some even said he's an idiot, he should have shut up about it, and now we're dredging this up all these years later. The burden was lifted that's what I needed to do. In prison g. Dep is still rapping. The only thing I want to talk about is walking out only because everybody else is talking about it. I tell them realistically i doubt it. 15 years is a long time when I've got to be strong, I did the crime. Said the system is insanity, i hope god forgives my calamity. For "nightline" I'm deborah roberts in new york.
This transcript has been automatically generated and may not be 100% accurate.