Transcript for The Underground World of Colombia's Child Sex Trafficking Trade
Good evening and welcome to this special edition of "Nightline." Tonight, we're going to take you inside a dangerous mission to rescue young girls caught up in the sex trade. This massive undercover sting is not being carried out by cops, but instead by a group of Americans that includes a former cia agent, a Hollywood star and a door to door salesman. They believe their modern day abolitionists, and tonight, you're going to see their commitment tested in the crucible of a violent Latin American city. And ABC's David Wright was there for all of it. ? Reporter: These Americans look like tourists heading out for a vacation romp. The clear blue water and those white sand beaches only part of the allure. The beauty of the surroundings here in Cartagena Colombia attracts many tourists. The beauty of the girls attracts many of men willing to pay. Especially those games. If you're messing with the girls -- they'll keep you up. I had this chick with me for two days. Reporter: These guys are supposedly here for a surprise bachelor party. Tim Ballard, the best man. In charge of the money. Marcus is a local tout who has been backing that he can arrange anything. What do we got? We got some new chickens? Yeah, what it is, I got six chickens. Reporter: Obviously they're not talking poultry. They're after girls for the big party and the younger, the better. But they have to speak in code because what they're looking to do, hire underage prostitutes, is illegal here. Marcus tells them to be careful. It's illegal. You can go to prison for that . Reporter: That's not to say he's unwilling to provide, if the price is right. Okay, of the girls that we already have that are sure, how many of them are actually minors? We have -- Seriously minors, I've got -- Yeah. Nine. What ages? I've got between 15 -- I got -- I got one 13, between 13 and 16 years old, I got. I've got one that's 13 right now. This is a Colombian operation, I want to make that very clear. Reporter: In truth, Tim Ballard doesn't want to buy these girls for sex. He wants to rescue them. What's your cover story? We're down here doing a big party, a bachelor's party from the United States. Rich guys. My best friend, I'm the best man in the wedding. And my buddy's coming down and we're going to surprise him with what we know he loves, and that's child sex. Reporter: Ballard is a former cia agent and former investigator for homeland security, specializing in human trafficking cases. I imagine your work to be the Liam Neeson character in "Taken." Yeah. I spent 12 years as a special agent for the United States government doing this. The problem is, the vast majority of the kids, we couldn't save. They weren't U.S. Cases, they weren't involved with the united States. Reporter: So, you formed your own organization? I created operation underground railroad. Reporter: He believes he's rescuing children from slavery. I'm a big Lincoln fan. We have it all planned out. Reporter: Operation underground railroad spent months organizing a massive sting operation in cooperation with Colombian authorities who are so overwhelmed with cases, they are happy to have help. The Americans are a believable group, because most of the pedophiles are sex tourists, according to this undercover investigator. He says that many are people with families and good jobs who come here for something exotic. It's 24 hours before the party. The team knows that tomorrow, anything can happen. Blow here, okay? And then you're pivoting. Reporter: So, they are going over basic hand to hand combat moves. Boom, boom, boom. We're not down here on vacation. We're down here to save children, okay? This can be a dangerous situation. I can pick you up and throw your on your held. Reporter: S.e.a.l. Team six this is not. A group of new recruits are here for the sting operation. All of them volunteers. Some of them asked us not to show their faces. But many, just regular civilians. Krista and drew are cross fit instructors from Utah. Back home, Tim works at at their gym. Christian is a fitness instructor and a door to door salesman. We have the cross fit trainers, we have the commercial real estate dude. The actor. Reporter: That actress is lawyer rh Laurie holden. Have you ever done something like this before? I spent time in Cambodia helping to get girls out of the brothels. I was trained by a Navy S.E.A.L. When I did "The walking dead." I can protect myself. Reporter: That's right. "The walking dead." Which is easier. This or killing zombies? We'll see. We'll see tomorrow. Reporter: The group has led sting operations before in other countries. We've been in the united States, we've been in Haiti, nick raragua Nicaragua, Guatemala, Ecuador. Reporter: What about this group? Are they legit? They're legit and very professional group. Reporter: The attache for homeland security investigations tells us this operation is not officially sanctioned by the U.S. Government. But the U.S. Is aware of it. I can imagine a lot of the viewers saying, geez, what a noble thing. Still being kind of skeptical. Because something that doesn't sit right, like, it feels like this should be the work of governments. It absolutely should be. If the governments were doing it, we wouldn't be trying this. No one's doing anything. And no one will do anything. We got them. Reporter: That's why they travel the world, gathering evidence to hand over to local authorities. A group of film makers have been following them, documenting their missions on hidden cameras for a new film, "The aboliti abolitioni abolitionists." Center stage for the Cartagena raid is this multimillion dollar mansion the group rented, nestled in the historic town center. Filmmaker Chad Thomas and his team wire the place for sound and video in order for the Colombian officials to prosecute the traffickers, they have to catch them red handed on tape. How much money are we talking about? $200, $300 for the evening for a child. Reporter: For weeks now, Tim and his team have been putting the word out to gather girls for the party. Thursday morning, the day of the party, at the mansion, they are getting everything set. Almost showtime, huh? Yeah. Reporter: Nervous? A little bit, you know, but that's good. I think it's going to be weird when we actually see the girls. It's going to set in, like, this is who has been sex trafficked. Reporter: Krista makes a sign to hang outside with balloons, like it's a teenager's birthday party. That's so that the traffickers won't seem out of place bringing so many young girls into the house. Some of the men splash beer on their faces and clothes. I want them to smell plenty of beer on men. Reporter: Actress Laurie's assignment is to keep the girls occupied in the pool area while Tim catches the traffickers on tape. A task that could take an hour. Try to keep the party going in a light, festive spirit, which will, guys, be the biggest acting challenge of all time. Our hearts are going to break the second they walk in. Reporter: Here, our fame could blow the group's cover. She's going to wear a brown wig, hoping to go incognito. It will work. Reporter: I wouldn't recognize you. Good. Hopefully they won't, either. Reporter: Several different potential traffickers will bringing girls to the party and their arrivals have to be perfectly coordinated. On the team, there are undercover operatives on the cti, Colombia's version of the FBI. Tensions running high. But there's a problem. One of the alleged traffickers is stuck in traffic. Five minutes behind schedule. Some of the girls are stuck in traffic, so, things are getting a little bit tense here. It all has to go off like clockwork or it may not happen. Five minutes! Reporter: They have to get the potential traffickers here and the girls in a safe place and every second counts.
This transcript has been automatically generated and may not be 100% accurate.