Federal investigators say they aren’t sure anything struck the windshield of an Amtrak train involved in last week’s deadly derailment in Philadelphia.

An FBI spokesman says agents performed forensic work on the locomotive Monday, days after the May 12 derailment that killed 8 people and injured dozens.

The FBI says it has ruled out that the windshield was struck by a firearm but is still investigating whether the train was hit by another object.

The National Transportation Safety Board says an assistant conductor told investigators she heard the Amtrak engineer talking to a regional rail train engineer and both said their trains had been hit.

Investigators say dispatch tapes didn’t have any communication from the Amtrak engineer reporting that his train had been struck.

Federal investigators say they’re months away from determining the probable cause of the deadly Amtrak train derailment.

The National Transportation Safety Board says any other reports on the crash that killed 8 people and injured dozens are “pure speculation.”

Investigators have said the train was traveling over 100 mph just before it entered a curve where the speed limit is 50 mph.

Amtrak resumed service Monday between Philadelphia and New York City.

Four passengers and a train conductor sued Amtrak over the crash Monday. The railroad has said it doesn’t comment on pending litigation.

(AP)