Emergency workers inspect the engine of a derailed Amtrak train in Philadelphia, Pennsylvania May 13, 2015. REUTERS/Lucas Jackson

WASHINGTON (Reuters) - The National Transportation Safety Board has concluded that the engineer of an Amtrak passenger train that crashed in Philadelphia in 2015 was distracted by radio traffic, NBC News reported on Monday, citing an unnamed source.

The derailment on May 12, 2015, killed eight people and injured more than 200.

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