By Patrick Rucker

WASHINGTON (Reuters) - U.S. federal investigators have found no record that the engineer of the Amtrak commuter train that crashed in Philadelphia last week reported an object hit his locomotive in the minutes before it derailed, a U.S. official said on Sunday.

The U.S. passenger rail service said on Sunday it would restore full service between Philadelphia and New York at 5:30 a.m. on Monday following last Tuesday's derailment that killed eight people and injured more than 200.

In an interview on ABC television's "This Week," National Transportation Safety Board member Robert Sumwalt said: "We listened to the dispatch tape, and we heard no communications at all from the Amtrak engineer to the dispatch center to say that something had struck his train."

The comment by Sumwalt comes as investigators are looking to explain what caused a circular pattern of damage found on the locomotive's windshield after the accident.

The NTSB has asked the FBI to help it examine the damage to the windshield, which is about the size of a grapefruit.

"This idea of something striking the train, that's one of the many things we are looking at right now," he said.

Sumwalt told CBS that investigators have all but ruled out the idea that a gunshot caused the damage to the windshield.

On Friday, investigators interviewed two assistant conductors and the engineer who was driving the train when it derailed.

One conductor had told investigators she may have heard the engineer say over the train's radio that something hit the windshield, Sumwalt said. But so far officials have found no independent corroboration of such a communication.

The engineer, Brandon Bostian, 32, who suffered a concussion in the crash, has told investigators he has no memory of what occurred after the train pulled out of the North Philadelphia station, just before the crash.

The train, which was barreling north at double the 50-mile-per-hour speed limit when it entered a sharp curve and derailed, was traveling from Washington to New York with 243 people on board.

Before Friday's disclosure about possible projectiles, the probe was focusing on why the train accelerated to 106 mph from 70 in the minute before it derailed.

The NTSB has not ruled out mechanical issues, human error or a deliberate act by the engineer, among other factors.

But Sumwalt said on Sunday that if the train was operating as it should, it would have taken a deliberate move by the engineer for the train to gain speed.

"The only way that an operable train can accelerate would be if the engineer pushed the throttle forward," Sumwalt said on CNN's "State of the Union."

Federal investigators were also looking into a report by the Southeastern Pennsylvania Transit Authority that an unidentified object hit one of its commuter trains in the area about 20 to 30 minutes before the Amtrak crash.

There is also an unconfirmed report by local Philadelphia media that a passenger on an Amtrak Acela train in the vicinity of the crash said a projectile had hit that train as well.

(Additional reporting by Peter Cooney in Washington; Writing by Frank McGurty; Editing by Chris Reese)