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IN NORTHERN SYRIA — A Texan who says he offered to work as an English teacher for the Islamic State and was captured earlier this month in Syria by U.S.-backed forces said he witnessed executions and crucifixions during the more than three years he spent with the terrorist group.

But 34-year-old Warren Christopher Clark, who is being held in Kurdish custody, told NBC News in an exclusive interview that he does not regret throwing in his lot with ISIS. No Kurdish security were present during the interview.

“I wanted to go see exactly what the group was about, and what they were doing,” he said. “Of course I saw the videos. I think with the beheadings, that’s execution. I’m from the United States, from Texas. They like to execute people, too. So I really don’t see any difference. They might do it off camera, but it’s the same.”

Warren Clark in a photo from his MySpace page. via MySpace

A Muslim convert, Clark was being held in northern Syria after being captured during the campaign to liberate the last pockets occupied by ISIS in Syria, the coalition of militias known as the Syrian Democratic Forces said. (For security reasons, NBC News is not identifying the town where Clark was interviewed.)

Clark, a former substitute teacher from Sugar Land, Texas, said the FBI has been in contact with him but he does not know what will happen to him next. He said he never fought for ISIS and said he was detained nearly a dozen times for refusing to take up arms.

Each time, Clark said, ISIS let him go and he suffered no abuse at their hands. But he admitted offering to work for them as an English teacher.

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NBC News reported last year that Clark's résumé was found at a house in Iraq and was later obtained by the Program on Extremism at George Washington University. In a cover letter, Clark said he was hoping to obtain a job teaching English to students in territory seized by ISIS.

"I was born and raised in the United States and have always loved teaching others and learning from others as well. My work background is largely in English and I consider working at the University of Mosul to be a great way of continuing my career," read the cover letter, which used the alias Abu Muhammad al-Ameriki.

The résumé included an email address, education credentials and work experience, and the researchers were able to determine that Abu Muhammad al-Ameriki was Clark, who graduated from the University of Houston.

"I was in living in Mosul at the time, and I needed a way to support myself," Clark said.

Clark says he was drawn to ISIS out of curiosity.

"I wanted to learn more about the ideology. I'm a political science major, global business minor. I like politics. I like travel, world events. That's what I wanted to do," he said.

But while Clark claims he was able to avoid fighting on the front lines, the war was never far away.

"It was a place that was constantly being bombed," he said. "You were always on edge. Day and night, just bombs and airstrikes. You sleep in the middle of the day. I spent most of my time living in a mosque. I just remember every day hoping not to get bombed."

Clark said he crossed into Syria from Turkey in June 2015.

The Texan was detained around the same time as two foreign militants from Pakistan, a fourth from Dublin, Ireland, and fifth man from Trinidad and Tobago, according to the Kurdish-led Syrian Democratic Forces.

The State Department said it was aware of "these open source reports" but gave no further comment.

Shiraz Maher, deputy director of the International Centre for the Study of Radicalization and Political Violence at King's College London, said there were conflicting reports on how many foreign fighters remained in Syria.

"Some have been captured, some have been killed and some are still alive and operational," he said.

Last year, a report by the Program on Extremism found that 64 Americans had traveled to Iraq and Syria in support of the Islamic State since 2011. This compares to the thousands of Europeans who joined ISIS during the same period.

Richard Engel reported from Northern Syria, Saphora Smith reported from London and Corky Siemaszko reported from New York.