Transcript for ATF Agent Goes Undercover in Prison
continues. Once again, David Muir. Reporter: Ask any of these hit men, these undercover agents, and they'll tell you by the time it gets to this -- You want him dead? Reporter: Time is running out. In many cases, the clock is ticking. The clock is definitely ticking. Reporter: Because you know that person's life is in danger. Because if they don't hire the fake hit man, they'll hire a real one. In every case, these men putting their own lives in danger. But, there was nothing quite like this -- as I understand it, several agents turned this job down. They did. I don't blame them. Reporter: Because to save the next target, Lenny has to give up his gun and do something extraordinary. But, not before doing trading his wife and two children at home and moving in some place else. The Warren county lockup in eastern Virginia, posing as an inmate. His new home, overcrowded. And filled with criminals. Murder, rape, robbery, arson. Reporter: And all of a sudden, you're in prison with all these guys. Now I'm in prison. Reporter: You were prepared to be there for how long? Months. Reporter: And here's why. The moment that started it all. Look in the driver's seat there. A drug dealer about to be busted. All right, got a white SUV on location. That's him. Reporter: The person getting in on the other side, a federal informant Dave Jackson who is buying drugs and helping the feds nab the bad guy. All right, by the time you get back, I'll be calling you. Reporter: The drug dealer is arrested, and now behind bars, he is fuming. He wants that snitch in the passenger's seat wiped off the Earth. If he can get the federal informant killed, then he's scot-free? He's scot-free. He gets out of jail. Reporter: The bad guy needs a hit man to get the job done. And when the feds hear that that drug dealer now behind bars is asking inmates does anyone know a hit man, that's when they decide to send Lenny in as a fake inmate, a fake hit man. And just look at the photo we brought our the interview. So this is Lenny, huh? That is Lenny. Reporter: They laughed. But, most wouldn't if they ran into someone who looked like this. His beard grown. Shackled, and in his new wardrobe, just one of his new uniforms. Here in his Orange jumpsuit. And posing as a hit man serving some time but about to go free. The story is, he'll soon be available to kill again. Lenny will never forget what they did to him moments after that door slammed shut. Because, remember, even the guards don't know Lenny is not a criminal. As we were getting ready to do the strip search, that's when I thought, "I didn't think this through. I didn't think this all the way." Reporter: You didn't sign. Through. Reporter: Up for that? Yeah, I was like, "I did not think this one through." Reporter: 20/20 going behind those walls, through the locked doors, straight to the cells where Lenny was thrown in with the criminals. Do you still remember the moment you walked into this place? Yes, I do. Reporter: What was going through your mind? As soon as that door closed you know, I was in it to win it at that point. Reporter: You booked him? I did book him. He was just Normal. Reporter: A Normal criminal. Minutes after arriving, Lenny quickly realizes this place is overcrowded. There is no bed for Lenny. And he has to steal a bunk from another inmate. So, you had 40 or 50 inmates sharing the space with you? Exactly. Reporter: You can hear the inmates just over the wall here. You had to find your own bed? Yeah, I just had to displace somebody else and take their bed to make theirs mine. Reporter: Displace somebody else? Right. Reporter: Remember, Lenny is here because that drug dealer somewhere in here wants to hire a hit man. But Lenny knows in order to nab him, he must now live the life of an inmate. So, this is where you were showering? This is exactly. Reporter: Give me an idea of where you're going to the bathroom. I'm using a communal toilet like this one right here. Reporter: In front of everyone. Including the security guards watching on surveillance. Inside we see some of the inmates have calendars scratched on the wall, crossing the off the days until freedom. The whole time, Lenny wondering, when his freedom would come. You know, you're hoping you're not going to end up the little spoon in a weird situation. Reporter: As a metaphor. Yeah, as a metaphor. Reporter: His worries soon replaced with adrenaline. Word comes that the bad guy, the drug dealer Jr Hackley, knows there's now a hit man behind bars right there with him. Listen to what's he's been told about Lenny. This guy has got bodies hanging on him. Reporter: This guy's got bodies hanging on him, means you -- Means I've killed people in the. Reporter: Many. And Hackley says? Hackley immediately contacts me. Reporter: And what does he say? I need this guy taken out. I'm like, "Well, what do you mean by taken out?" "I need him gone forever; I need him, you know, eliminated." Reporter: And you're thinking -- I'm thinking this is a home run. Reporter: But, in this high stakes game, a sudden curve ball. Because, while all the guards and inmates believe Lenny is a real criminal he knows the one thing protecting him are the surveillance cameras. But, then a huge storm hits. Every one of those cameras knocked out. Suddenly these cameras go dark. Lenny has no idea. I'm in here without cover, without any backup. Reporter: But, incredibly even in the dark, listen to how quickly things move. He meets the criminal. Plays the role of the hit man. And he's hired for the job. Sxwlr how is he going to pay you? With a motorcycle. Reporter: And within hours that cover team gets him out. Now all that's left is the murder. He's off to the murder scene. And right there waiting, the guy he's supposed to kill. The federal informant who while sitting in that car buying drugs now talking to 20/20. In order to convince him that you were dead, they concocted a plan? They came to me and said, "Look, we're going to fake your death." Reporter: But, even before federal agents can give him the script he turns out to be quite an actor. I said, "I -- I got this." Reporter: He tells them what a drive-by shooting should look like. And this is the photo they took proving the hit man had done his job. The snitch snuffed out. And look at this. As proof that they killed him. They take that photo and insert it putting it on the front page of a real newspaper giving it a headline. "Unidentified man found shot to death." And they're about to take that newspaper to the criminal who wants him dead and just listens to what he says -- I owe you my life, you know I do. Reporter: A proud drug dealer staring at a headline, now staring at 25 years in prison because of it. For Lenny it is another triumph. As he now prepares to return to his other life as a dad of two. As we walk through the neighborhood where that murder for hire plot was concocted. Hits are playing out in neighborhoods all across America. Yeah, that's true. Reporter: Plans are being hatched with kids playing outdoors. Yep. We're in middle day, modern America and you have kids playing all around you and there's nefarious individuals planning out murders and hits. Reporter: And as Lenny goes home, ken is back on the road too. Living that double life. What does he tell his own children? What does he tell the other parents? So, when you're at a soccer game or a school event and another parent says, what do you do? Every once in a while I'll get somebody who will ask and you keep things vague. Reporter: What do your kids know? Probably more than I would hope that they would know. Reporter: And for the first time hit man the rookie who caught that suburban mom in a supermarket parking lot, a simple question tonight. You could be on a new case tomorrow. Yes, I can. Reporter: Or today. Or today. Or after this. Who knows? Yeah. Wherever the job takes me. ?
This transcript has been automatically generated and may not be 100% accurate.