The terrorist who detonated a bomb outside Kabul’s international airport on Thursday, killing at least 170 people including 13 U.S. servicemen, waited until he was as close as possible to American troops, according to officials cited by The New York Times. The suicide bomber detonated a 25-pound explosive vest, an unusually large device, just as he was about to be frisked by U.S. troops manning the airport’s Abbey gate. Gen. Kenneth F. McKenzie Jr., the head of United States Central Command, previously said that the explosion happened at an “interface point” where evacuees who have gone through initial screening by the Taliban are then hand-searched by U.S. troops before they can get on flights. “Ultimately Americans have got to be in danger to do these searches,” he said. The Times reports that the Taliban had twice pushed crowds back from the outer perimeter on Thursday but the bomber somehow made it through in a third surge of people.