unexploded ones. they're hoping to find the bomb maker's signature for what remains of these explosives. there is a navy bomb detonation team here helping with the investigation. no surprise. a lot of people on the team telling me it felt like an ied attack seen overseas. barbara star is at the investigation covering this. >> good morning, john. you said bomb signature. what does that really mean? what are investigators focusing on? what we know is, in fact, just as you said, john, after years of war, the military and the fbi civilian law enforcement have a tremendous amount of expertise in looking at these blast scenes. it really is something like you see in afghanistan or iraq. looking at what is left after the bomb explodes. one of the things that happens is bomb makers over time tend to put their bombs together the same way. and that is the bomb maker's signature. so they're looking at how was the bomb put together? what are the parts?