Sept. 11 attackers: tourist, business and student visas
The paths to violence for the United States-born attackers varied. Some were recent converts to Islam. At least three who were born in the U.S. had previous criminal histories, and one had a history of mental illness. One seemed to have radicalized after spending time in Yemen. Another became radicalized after being convicted of lying to F.B.I. agents denying he had made plans to travel to Somalia when in fact he had.
Security experts argue that the risks of routine travel including the U.S. visa waiver program, which allows citizens of Britain, France, Belgium and 35 other countries to enter the United States without a