 -- In a shady corner of beautiful historic Cartagena, Colombia, two men sit in an open café, bartering over the price of sex with several young girls with an alleged sex trafficker named Marcus Bronschidle.

But what Bronschidle didn’t know was that the guys he was talking to didn’t actually want to buy young girls for sex. Instead, the whole encounter was secretly recorded as part of a child sex trafficking sting operation.

They are a part of an organization called Operation Underground Railroad, led and founded by Tim Ballard. Ballard is a former CIA agent and former U.S. Homeland Security investigator who specializes in child sex trafficking cases.

“I spent 12 years as a special agent, undercover operative for the United States government, doing this, and learned how to do it,” Ballard said. “The problem was that the vast majority of the kids that we would identify, we couldn't save. They weren't U.S. cases.”

For months, the group put together a massive sting operation in cooperation with Colombian authorities. They each had an elaborate cover story. Ballard’s story was that he was the best man in a wedding back in the U.S. and was looking to hire several underage prostitutes for a big bachelor party in Cartagena. The cover was meant to lure the sex traffickers into a setup so that Ballard and his team could rescue the girls, many of whom were under 18.

Ballard’s team features a ragtag group of volunteers, some off-the-books operatives and one former Navy SEAL, but many just regular civilians. There are two CrossFit instructors from Utah, a door-to-door salesman, and even Hollywood actress Laurie Holden, who starred in “The Walking Dead.”

A group of filmmakers, led by Chet Thomas and Darrin Fletcher, have been following them, documenting the missions on hidden cameras for a new film, "The Abolitionists" and gathering evidence to hand over to authorities.

Center stage for the Cartagena raid was a multi-million dollar mansion the group rented for the “bachelor party.” Visual and audio evidence is crucial for investigators to be able to prosecute the traffickers. Thomas and his team wired the entire house with hidden cameras for sound and tape.

Prostitution is legal in Colombia and widespread, but the country’s tolerance for prostitution does not extend to children or the people who traffic in children. Those who do face up to 16 years in prison.

In order for Colombian officials to prosecute the sex traffickers, they have to catch them exchanging money for the girls on tape.

“It’s going to be about $200 to $300 for the evening, for a child,” Ballard said.

On the day of the party, Ballard’s team got the house ready. They even hung a sign outside with balloons, like a teenager’s birthday party, so the traffickers wouldn’t seem out of place bringing young girls into the house. Once the girls arrived, Holden’s job was to keep them occupied by the pool area while Ballard and the undercover officers worked to catch the traffickers on tape exchanging money. Colombian authorities quietly hid, waiting for Ballard’s go sign to move in and bust the party.

Then the sex traffickers started to arrive with the girls. Unaware that hidden cameras are rolling or that police were waiting, Bronschidle, one of the sex traffickers, talked up one of the girls, who he said was 14 and was ready for “everything.” Ballard, still undercover in his role as the best man, waited for him to make the move that would put him away in prison and save the girls.

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