terrible injuries and hospitals reported seeing shrapnel wounds. >> there's a lot of small metal debris. some people have -- have asked already about whether these were bbs or parts of bombs. i just don't think we're able to say whether these were small bits of metal placed there intentionally or part of the environment. >> reporter: shrapnel is just one of the clues investigators will be looking at. >> there are fragments everywhere, there are fragments everywhere, there are fragments within the victims. fragments in the sidewalk. what they're going to be able to do is probably reconstruct the timer device, what was used, they're going to look at the components of the bomb, able to tell them is this just somebody that put this together over the internet or is this a bomb maker? >> reporter: hundreds of state and federal investigators have descended on boston to try to find out who could have built the bombs and set them off. >> there are federal, state and local law enforcement all on scene and coordinating very close ly. the fbi has taken charge of the investigation. >> reporter: this type of attack