and they can actually, these machines, detect a trillionth of a gram of residue. so they're very, very good. >> the group that is believed to have the highest level of bomb-making expertise is aqap. that's essentially al qaeda in yemen. tell us more about them and how they developed this expertise. >> al qaeda in yemen are at the center of the concern when it comes to this threat. they are significantly ahead of isis when it comes to developing sophisticated devices, concealing bombs inside electronics. they have a master bomb maker ibrahim al asiri, a saudi who's very good at building these kind of devices. and for years has been developing underwear bombs, shoe bombs, even the group has experimented with surgically implanting devices inside people so that they can get them on planes. there's intelligence that's come out on that. and this is a group which is believed to have shared this technology with a number of