FBI investigators say they'll check whether or not a bullet made a mark on the windshield of Amtrak Northeast Regional Train 188. Federal investigators, meanwhile, said there was no record of the engineer reporting an object hitting the locomotive moments before the May 12 deadly derailment.

On Monday, Amtrak resumed Northeast Corridor service between Philadelphia and New York for the first time since the crash that killed right and injured scores of passengers. The first trains left the cities before 6 a.m.

"Our infrastructure repairs have been made with the utmost care and emphasis on infrastructure integrity, including complete compliance with Federal Railroad Administration directives" CNN quoted Amtrak President and CEO Joe Boardman as saying in a statement.

Thousands of commuters spent almost a week using alternate ways to travel between Philadelphia and New York. Transit officials said that, even though the service resumed, there could be some cancellations and delays.

Train 110 was delayed for 16 minutes as it left Philadelphia's 30th Street Station at 6:09 a.m. Monday. Philly.com reported that a number of early-morning trains got canceled.

The National Transportation Safety Board asked the FBI to find out what damaged the windshield. At least two more trains reported having been hit with projectiles: an Amtrak Acela train and a regional Septa (Southeastern Pennsylvania Transportation Authority) train.

NTSB board member Robert Sumwalt said he was not sure if something had hit Train 188 before the derailment. He said that the Amtrak engineer had not reported any such incident. The Septa engineer reported to a dispatcher that his train had been hit by something, he said.

Amtrak engineer Brandon Bostian has claimed that he does not remember anything about the derailment. According to Sumwalt, it was reasonable for him not to remember details about the accident.

Sumwalt told CBS that the windshield damage did not look like that it had been hit by a bullet. The damage to the windshield was like the size of a grapefruit, he said.

Contact the writer: s.mukhopadhyay@ibtimes.com.au