The Amtrak train that derailed north of Philadelphia was struck in the windshield by an unknown object shortly before the horrific crash, an assistant conductor told investigators on Friday.

A few minutes after leaving Philadelphia, the 39-year-old Amtrak conductor overheard a local commuter train engineer tell her motorman, Brandon Bostian, over the radio that his train had been “hit by a rock or shot at,” officials said.

Bostian then told an engineer on the local SEPTA line that his own train had also been hit by an object, according to the conductor, who is not being identified by the National Transportation Safety Board.

“Right after she recalled hearing this conversation between her engineer and the SEPTA engineer, she said her train leaned over on its side,” NTSB spokesperson Robert Sumwalt said at a press conference.

The Amtrak train was traveling at 106 mph, more than double the speed limit, when it approached a sharp curve and ran off the track.

NTSB investigators are calling in the FBI to probe a “circular pattern” in the lower portion of the left-hand windshield that doesn’t appear to be caused by Tuesday’s crash.

The commuter train was struck just after passing through a station in North Philadelphia, roughly two miles from the crash site.

Bostian, who hadn’t reported feeling fatigued or sick that day, said the last thing he remembers is ringing a bell at the North Philadelphia station, signaling that his train was passing through.

He was on the second leg of his round-trip New York City-to-Washington route at the time of the crash. He’d been working that route for “several weeks,” Sumwalt said.

“We found him to be extremely cooperative,” he added.

Meanwhile, Amtrak, in a blog post by President and CEO Joe Boardman, has apologized and took “full responsibility” for the crash that killed eight people.