Eight people were killed and more than 200 passengers injured when Amtrak Train 188 derailed in Philadelphia on May 12.
The Federal Bureau of Investigation was called to determine if a projectile had hit the train before it derailed.
But the National Transportation Safety Board announced yesterday that the FBI had found "no evidence" of any damage to the train's windshield "that could have been caused by a firearm."
The woman also said she heard over her radio that a separate train had been "hit by a rock or shot at," causing that engineer to make an emergency stop.
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The NTSB said it has "not ruled out" the possibility that "another object may have struck" the doomed train's windshield.
The entire investigation would take up to a year but additional updates would be announced later this week, the NTSB said on its Twitter account.
The four-count lawsuit accuses Amtrak of causing the "tragic and preventable" accident through "reckless operation on the tracks and (an) inexcusable decision to not include a necessary safety system."
The train was travelling at more than 160 kilometres per hour -- twice the speed limit -- when the driver slammed on the emergency brakes just before the crash.