potentially help investigators identify who was responsible, whether it's an individual or a group, and what their motivation was. >> now, we've heard about these before, fran, right? faz faz fazel shazad, used some type of pressure cooker device. how big is the universe of someone who could make something like this? >> studies have been done looking at successful and unsuccessful terrorism plots in the united states and when you look, the perimeter really is striking. you start where the device exploded and work your way out. time and again, investigators found there is always -- these devices themselves are actually the final construction of it, near -- very near to -- within miles of the bomb site itself, and so the investigators will