The FBI will investigate the possibility that the windshield of the Amtrak train that derailed this week was struck by some kind of projectile before it crashed, the Associated Press reports.

According to the AP, at a press briefing on Friday night, National Transportation Safety Board member Robert Sumwalt said that there were concentric circles on lower left corner of the train’s windshield, indicating that something had struck it before it was shattered in the crash.

The New York Times reports that Sumwalt, who is leading the NTSB’s investigation into the incident, said that Brandon Bostian, the train’s engineer, was asked whether he remembered anything hitting the train. “He did not recall anything of that sort,” Sumwalt said. “But then again, he reported that he does not have any recollection of anything past North Philadelphia.” (Otherwise, Bostian has been “extremely cooperative.”)

There have also been reports that something hit a Septa train in the area that same night, and the derailed Amtrak train’s assistant conductor said that she had heard Bostian talking to a Septa engineer, according to Sumwalt. From the Times:

She said she thought she heard Mr. Bostian reply that his train had also been struck.

“Right after she recalled hearing this conversation between her engineer and the Septa engineer, she said she felt a rumbling, and her train leaned over and her car went over on its side,” Mr. Sumwalt said.

Jerri Williams, a spokeswoman at Septa, confirmed that the windshield of one of its trains had been shattered by a projectile near the North Philadelphia station about 9:10 p.m. on Tuesday, about 12 minutes before the Amtrak train derailed.

The Federal Bureau of Investigations has been called in for its forensics expertise, Sumwalt said, but it has not yet begun its investigation.

Photo credit: AP Images. Contact the author of this post: brendan.oconnor@gawker.com.