the fbis investigating. that's a misnomer. we are investigating. we asked the fbi to come in and provide technical expertise to help us resolve and figure out what was a particular damage pattern on a windshield. we are investigating it at this point. we asked them to come in and help us out on identifying the fracture pattern. >> bring in tom costello, just outside the 30th street station in philadelphia. tom, it seems the ntsb is trying to tap the brakes on this growing story that maybe some outside entity or force caused this accident. >> reporter: well, here is why they're concerned about this. they had the train hit by something. the train conductor thought he was shot. another train was hit by a brick or something and this amtrak train 188 hit by something on the windshield. nobody knows the answer to this