An investigation into a commuter train derailment in New York last December, which killed four people, has found the driver had a serious sleep disorder.
The National Transportation Safety Board has released its report into the derailment.
NY commuter train wreckage after derailment. Photo: AFP
The BBC reports that it has found that the train driver William Rockefeller was found to have "severe obstructive sleep apnoea".
However, officials have not said whether the condition contributed to the crash.
The Metro-North train, which was travelling from Poughkeepsie to New York's Grand Central station, was travelling at nearly three times the speed limit on a bend when it jumped the tracks.
More than 60 people were injured as it derailed and came to a stop a short distance from the Harlem River in New York's Bronx borough.
Sleep apnoea
During a sleep evaluation after the crash, Mr Rockefeller was found to suffer from the medical condition sleep apnoea, in which breathing is briefly, repeatedly interrupted during sleep.
More than 18 million American adults experience sleep apnoea, according to the National Sleep Foundation.
Mr Rockefeller's lawyer and union leader have previously suggested the engineer fell asleep as the train entered a sharp curve before derailing.
The NTSB has said it will release its determination of the cause of the accident in a later report.