The engineer of a commuter train that slammed into a station going double the 10 mph speed limit, killing a woman, suffered from sleep apnea that had gone undiagnosed, two U.S. officials told The Associated Press on Wednesday.

One official said investigators are looking at it as a potential cause.

The officials, who were briefed on the investigation, spoke to The Associated Press on the condition of anonymity because they weren’t authorized to discuss the matter.

They said the engineer, 48-year-old Thomas Gallagher, was diagnosed with sleep apnea after the Sept. 29 crash in Hoboken, the officials said.

Sleep apnea robs its victims of rest because they are repeatedly awakened as their airway closes and their breathing stops, leading to dangerous daytime drowsiness.

The same condition went undiagnosed in the engineer of a commuter train that sped into a curve and crashed in New York City in 2013, killing four people.

A union representing Gallagher didn’t immediately respond to a message seeking comment. NJ Transit also did not respond to a message.