Transcript for Undercover and Hired to Kill
Tonight, a stunning network exclusive. For the first time a group of hit men coming forward together and sitting down with "20/20" and they have a giant secret to reveal. These hit men are actually undercover federal agent and who's hiring them, tonight, exclusive surveillance video from the suburban soccer mom with specific instructions to the other case of a husband with a plot of his own. And you're about to see it all unravel. Reporter: In every corner of America right now, people with criminal minds and black hearts are plotting, looking for someone to do their dirty work. A scorned lover, husbands who want their wives dead, women who want their husbands taken out. Even children plotting against their own parents. She tried to hire a hit man to kill her father. Reporter: Tonight, we go inside the secretive and very real world of murder for hire. Just listen to this wife. What do you want done? I want him more than hurt. I understand you want him dead? Yeah. Reporter: Then there's this Massachusetts husband who wants it done and quickly. I'm not playing any kind of games here, all I want is mission accomplished. You take care of business and we go our separate ways. Reporter: And the Michigan wife who wants her husband gone and doesn't care how ugly it gets. As long as it's not in the house. So you don't want it done in the house then? 'Cause it would be messy in the house. Reporter: All of them ordering a hit like most of us order dinner tonight. In last month, more than 30 cases of murder for hire making national headlines. One a day. And those are just ones we know about. And then there's Guillermo vasco, the young husband who married a pretty doctor from Massachusetts. And what you're watching is the surveillance video of him about to hire a hit man to kill his wife. My wife betrayed me. I'm gonna make it look like she disappeared. Exactly. He wants her killed and buried ten feet under. How soon did he want her dead? As soon as possible. Do you want it to be painful or do you want it done quick? For her. Reporter: Ken is the hitman hired by Guillermo and tonight he's not the only one coming forward. A group of his comrades, all men boarding planes, getting into their cars and on their way to sit down exclusively with "20/20." But these men all have a secret. They are undercover federal agents with the ATF posing as hit men. They meet us at ATF headquarters in Washington, D.C., where we have makeup artists waiting. They sit down to have their appearances completely changed. I'm feeling my feminine side coming out. Oh, there's nothing feminine about the brows I'm about to give you. You're not going to want to wear that out tonight. Reporter: Prosthetic noses. Cheeks. Facial hair. The disguises, the only way they can truly reveal what it is they do. Jeanne Marie laskas knows the stakes. She's reported on their hidden world for "Gq." This is really extreme cop work, heroic cop work that the public does not know about. You've got 30 minutes. Reporter: Our clock rolls and after more than three hours they are ready. We have never seen an entrance quite like this. Walking in to sit down with us. Gentlemen, good to see you. Welcome. Nice to meet you. Reporter: The agents offer up first names only. Jose? Yes. Reporter: And? I'm Lenny. Reporter: Lenny? Your real name? Real name. Ken. So just a show of hands. How many of you are in a disguise today? All but one in disguise. Lenny, the only one no longer working undercover. Their appearances so transformed, so over the top, even these hardened agents are humored. I mean, when you look in the mirror with that getup, does it shock even you? Yes. Yes -- Reporter: But -- but those are the stakes? Right. Reporter: Did any of you send a photograph to your wife? I sent a photograph. Yes. Reporter: One agent tried to facetime with his wife and baby boy right before our interview. He just had this crazy look on his face like he didn't know who I was. Reporter: As for ken's wife? What did your wife say? She found it very entertaining. She said I was a cross between a biker and a lion. Reporter: And while the disguises may look comical, the very real danger these men face is no laughing matter. 'Cause you'll be back on the street tomorrow? Yes. There have been a lot of ATF agents who have actual hits attempted on them. What are people looking for? I mean, what do they want in good hitmen? Reporter: But how do you find a hitman? I mean, you're not in the yellow pages. There's no phone number, no post on craigslist. It's a business like so many others that thrives on referrals. Which brings us back to that husband, Guillermo vasco, who -- behind bars -- started asking around for a good hit man, to kill his beautiful wife. But how does he want her killed? He wants her killed slowly. And he wants her to suffer. He -- He says that? Yes. Reporter: And why? It turns out Guillermo vasco came all the way from Ecuador to America to marry that wife, a Massachusetts doctor he'd met while she was visiting his country. They would have a baby together. But authorities say when the wife started to see behavior that worried her and wanted out of the marriage for good, he showed up at the door to win her back. When she says, "We're not getting back together?" He kneeled down in front of her and out of nowhere took a piece of duct tape and put it right over her mouth and had a knife. And he said, "You have to listen to me." Reporter: Sergeant Sheila Mcdaid says he attacks her,ir 2-month-old baby right there. He had a five gallon can of gasoline with him and he said, "This house is where all our problems started and this house is where it's gonna end. We're - - we're all gonna die. We're gonna go to heaven today." Reporter: But she breaks free and escapes with her baby. Guillermo is arrested. Now sitting in prison a year after that arrest, and he is still working to kill her. He doesn't want her testifying against him at trial. She thought it was behind her though, didn't she? Yeah. She thought that he's gonna be put away for a long period of time. But when asking around for a good hit man, Guillermo makes a critical mistake and asks another inmate, a snitch, who tips off authorities at the ATF. How do you get wind that he wants to hire this hit man? I had a confidential informant in the jail, someone worked for us in the past, someone who'd provided reliable information in the past for us. Initially he wanted both the wife and the infant daughter killed. We developed a plan that we were going to have an undercover secret agent pose as a hit man and go into the jail and meet vasco one on one face to face. Reporter: And that hit man is ken wearing a hidden camera, sitting right across the table from Guillermo as that husband pulls out a letter he'd written using a special code, in case it ended up in the wrong hands. He talks about his wife as a? Old dog. And the infant as a? Puppy. Reporter: So he's talking about his family as a couple of dogs? Yes, exactly. "Is too old. Won't be able to make the trip." Nikki is very old and she's sick. She won't survive the trip. We need to put her to sleep. Reporter: And that's code for? Kill my wife. Kill my wife? Yeah. Reporter: And incredibly, listen as he offers instructions right down to how he wants her buried. If we can bury her out of Massachusetts, would be just perfect. Yeah, you know, probably go north. Because Maine, not many people up there, lots of woods. Uh, so yes, uh, just make sure that the body be more than ten feet down. So she doesn't show up again. Do not forget the cement. Do you really want her in cement? Yes. To keep her down? Yeah. Reporter: When somebody hires a hit man, they're looking for someone who's going to encourage the job, go along with it. Right. If they say, "You know I want them, you know, their throats slit and buried over here," you get that conversation, you may throw out another idea like, "Well, what do you think about this?" I'm a hit man. I have to have ideas. What do you think about putting her in the water? In the water they disappear. She goes in, you load her into one of those drums, you know weigh them down, get them down they get eaten, there's not much left. You know? Reporter: Done. She'll be killed in the woods, stuffed into an old drum and dumped at sea. Watch as the husband goes over pictures of the wife's house where she's now raising their baby. And then pulls out his own hand-drawn floor plan to help the hit man. And now, the money. What does he offer you? He offers me a rare coin collection that he said was worth thousands of dollars. Reporter: And this whole thing is being recorded? Yes. Reporter: Outside those prison walls, agent Matt o'shaughnessy hears the plot, the payment, but it turns out he wants more. So, you're about to take this much further? Yes. Reporter: You won't believe who they are about to enlist for help. So you approach his wife? To put her husband away for good. She wanted to nail her husband?
This transcript has been automatically generated and may not be 100% accurate.