not a new relationship. the fbi obviously has been asked to come in and analyze that damage. and try and i had tiedentify what might have actually hit the train. the question is whether that whatever hit the train was accidental to the accident or directly relate to the accident itself. denieding on ing depending on their analysis will affect the direction the accident investigation takes. >> here is how robert sumwalt described the damage. let's listen. >> if you're standing in the middle of the locomotive cab over here is the engineer's wind shield, here the other. and lower portion of the left hand windshield, there is a circular pattern that emanates out just a bit. >> what are the factors that investigators use in trying to determine what caused that