So that leaves physical medical issue, mental or emotional problem, or something out of his control like a sabotage.
Via Daily Mail:
The engineer who was operating the train that crashed into the Hoboken, New Jersey station on Thursday was not under the influence at the time of the accident.
Conductor Thomas Gallagher, 48, underwent a blood test, which came back negative for drugs and alcohol, a law enforcement official told ABC.
Authorities have already recovered one of the train’s two black boxes as the National Transportation Safety Board tries to determine the cause of the crash that killed one and injured 114 others.