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 comment by Robert Sumwalt, a member of the National Transportation Safety Board, comes as investigators are looking to explain what caused a circular pattern of damage found on the locomotive's windshield after the accident.

"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," Sumwalt told ABC television's "This Week." Sumwalt spoke on several television networks on Sunday.