Could this have caused the derailment?
Check it out:

The FBI will examine the windshield of the locomotive that derailed in Philadelphia, trying to determine if it was damaged by a projectile or a bullet before this week’s fatal crash, National Transportation Safety Board member Robert Sumwalt told reporters Friday night.

This latest twist comes after an assistant conductor told investigators she believed she had overheard the train’s engineer talking about something striking the train, Sumwalt said.