A lawyer for the engineer of a New Jersey commuter train that crashed in Hoboken in late September, killing one person and injuring more than 100 others, said his client has since been diagnosed with severe sleep apnea, which can cause drowsiness.

The disclosure came six weeks after officials of the National Transportation Safety Board (NTSB) said the engineer had told investigators who interviewed him that he was fully rested at the time of the train wreck but had no memory of it.

Jack Arseneault, a lawyer for the engineer, Thomas Gallagher, told Reuters on Wednesday that after the crash his client was "examined and tested and found to have severe sleep apnea."

NTSB spokesman Christopher O'Neil said he could not confirm whether the engineer suffered from sleep apnea, but added the agency was looking at whether any "undiagnosed conditions exist that could have contributed or impaired the worker."

Arseneault said he turned over the findings to the NTSB on Oct. 31. Gallagher, 48, was examined in July by an New Jersey Transit doctor and found to be fit for duty, Arseneault added.

The diagnosis could help explain the cause of the Sept. 29 crash. The disorder, characterized by shallow or interrupted breathing during sleep, often goes undiagnosed and can result in poor quality sleep, leaving sufferers fatigued during the day, according to the U.S. National Institutes of Health.

The NTSB said in a preliminary report last month the brakes were working on the train that crashed into the station, killing a woman who was standing on the platform and injuring 110 other people.

The train was traveling at 8 miles per hour (13 kph) 38 seconds before the crash, then accelerated to a speed of 21 mph (34 kph) at impact -- twice the speed limit -- and that emergency brakes were applied one second before the crash, according to the report.

Investigators have found no mechanical issues with the signal and train-control systems, the report said.

Federal officials briefed members of Congress on aspects of the investigation on Wednesday.

In 2014, the NTSB said the driver of a train that derailed in New York City, killing four passengers, had an undiagnosed sleep disorder at the time of the 2013 accident.

New Jersey Transit is the third-busiest U.S. commuter system, handling nearly 1 million bus and rail passengers a day.

(Reporting by David Shepardson; Editing by Steve Gorman and Simon Cameron-Moore)