BOSTON (AP) — A passenger door on a Boston subway car did not function properly when a man got his arm stuck in it and was dragged to his death last month, federal investigators said Monday.

The trains are equipped with safety features to prevent them from moving when the doors are obstructed, the National Transportation Safety Board wrote in the preliminary report.

“NTSB investigators examined and tested the railcar involved after the accident, identifying a fault in a local door control system that enabled the train to move with the door obstructed,” the report said.

The man, identified by local authorities as Robinson Lalin, 39, of Boston, died around 12:30 a.m. April 12 as he exited the six-car Massachusetts Bay Transportation Authority Red Line train at the Broadway Station.

“In the attempt to exit the train, the passenger’s right arm was trapped in the door,” the NTSB report said. “The train departed the station, dragging the passenger along the platform about 105 feet and onto the surface below, near the tracks.”