The top Democrat on the House Intelligence Committee says at least one foreign fighter for the Islamic State of Iraq and Syria has already traveled in and out of the United States before committing a suicide bombing overseas.

Rep. Dutch Ruppersberger, D-Md., cited the example as one of the reasons the intelligence community is so concerned about Americans and other Westerners going to fight for Islamic State and returning home to carry out a terrorist attack on U.S. soil.

“There was an American that went over and he was radicalized, trained to be a suicide bomber and he came home to see his parents, left, went back and when he went back he killed himself and a lot of people,” Ruppersberger told the Washington Examiner on Tuesday, declining to elaborate with further detail.

“That’s an example. What’s concerning to us is when you have a passport, you can go back and forth with impunity,” he said.