This episode of True Spies contains graphic details related to the sexual abuse of children that listeners may find disturbing.

Welcome to True Spies. Week by week, mission by mission. You'll hear the true stories behind the world's greatest espionage operations.

You'll meet the people who navigate this secret world. What do they know? What are their skills? And what would you do in their position?

This is True Spies. I literally thought that it would be much better for me to go back in there with a grenade and just pull the pin and blow all of us up in that room.

And I had to fight those urges. I was going to have to sublimate my hatred and disdain for what they were espousing if we were going to make this case successful.

This is True Spies. Episode 42. Inside Nambler.

There are many surprising places that a life undercover might take you.

I posed as a contract killer, as a drug dealer, both as a high roller drug dealer and a street level drug dealer.

It was a white collar criminal, been an international arms dealer.

In his 26-year-long career as a street agent in the FBI, Bob Hamer was thrown more than a few curveballs.

I've been shot at, I've shot people. I've had a contract put out on my life, I've had a gun put to my head. But never anything that ripped at the fabric of my soul.

Until that is, he found himself walking through Manhattan one evening, shoulder to shoulder, with a new type of target.

We assembled about 25 or 30 of us and we banned a walk from Grand Central Station to Times Square.

This stroll through the big city is Bob Hamer's first face-to-face contact with the organization he has been stalking for more than a year.

As we were getting a little closer, I could sense the excitement. It was almost like when you go to the big game.

And as you know the game is about to start and you begin to find your seat and you can just sense this excitement.

I could sense the excitement that these men were feeling and I didn't understand it.

To the casual observer, they might be a group of businessmen on their way to dinner to blow off steam after a day at a dull conference.

But that destination was no restaurant, no theater.

And then we walked into Toys or Us.

And they literally ran to a 60-foot indoor Ferris wheel. They ran to the railing and they looked over the Ferris wheel and they watched these little boys that were in the Ferris wheel going around on this ride.

And I sat there and I listened to some of these men talk about what they wanted to do to little boys.

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