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On "America's Newsroom," the first undercover Muslim FBI agent to go public spoke out about his work infiltrating Islamic extremist groups.

Tamer Elnoury - one of the active agent's multiple false identities - told Bill Hemmer that he was working as a police officer in New Jersey, and he was recruited by the FBI after 9/11, as the bureau realized it needed more Arabic speakers.

He said radical Islamic terror does not represent his faith, so he wanted to dedicate his life and career to combating that evil.

"When we have a subject that we suspect has ill intentions toward our country, is a threat to our nation, I get to study him, I get to learn his pattern of life, I get to find the best person I can be to insert myself into that life as quickly as possible, in an effort to properly gauge that threat," Elnoury said

One of his undercover operations involved befriending Tunisian migrant Chiheb Esseghaier, who planned to kill as many people as possible by derailing a train traveling between Toronto and New York City.

"We wanted to give him a like-minded brother that sympathized and had the same ideology as him, so that he could trust me in time [and] reveal his plans," Elnoury said.

During a trip to New York City, Esseghaier stayed near Ground Zero, where he told Elnoury that the U.S. "needs another 9/11, and we're going to give it to them."

"That was the first time in my career that I had a physical reaction to something a subject says," Elnoury said. "9/11 was so personal to me, so personal to all of us. And for him to stand there say what he said the way that he said it, I almost lost myself that night."

Esseghaier was arrested in 2013 before he could carry out his planned attack. He was sentenced to life in prison in 2015 thanks in part to Elnoury's undercover work.

Learn more about Elnoury in his book, "American Radical."

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