When he checked in for his flight to Boston, Egyptian national and 9/11 mastermind Mohammad Atta was selected for additional scrutiny by a computerized prescreening system called CAPPS (Computer Assisted Passenger Prescreening System). However, under security rules at the time, the only consequence of Atta’s selection was that his bags were scrutinized. He was not. Nine of his fellow al-Qaeda hijackers similarly managed to evade the enhanced security checks at other airports even though CAPPS flagged them. They proceeded to board three of the four planes used to carry out suicide strikes on September 11, 2001.