The bombing at the kabul airport in august that killed 13 u.s. service members and at least 170 afghan civilians was the result of a single bomber. not a complex attack as the united states military thought. the pentagon shared the results of the month s long investigation. that attack happened when the u.s. and foreign troops were conducting evacuations. oren liebermann joins us now. what more are u.s. officials saying about the investigation. investigators have been interviewing scores of u.s. witnesses and coalition forces to get a better sense of exactly what happened during, before and after the attack. in the conclusion of that investigation, they say that the attack itself could not have been prevented. they say the bomber likely used alternate routes to get to the ab gate of hid karzai international airport to avoid taliban checkpoints and it was