The Metro-North driver at the controls during a derailment that killed four and injured more than 70 suffers from a sleep disorder, The New York Times reported on Monday.

The National Safety Transportation Board on Monday refused to comment on the Times report, saying a review of the December 1, 2013 accident has not yet been released.

According to the Times, the driver, William Rockefeller, suffered from sleep apnea, which could have been aggravated by his recent change to the 6 a.m. shift on November 17. Sleep apnea is a chronic condition that can result in drowsiness during the day, according to the National Institute of Health.

Shortly after the derailment, representatives for Rockefeller said it seemed that he had fallen asleep as the train neared the sharp curve at the Spuyten Duyvil station around 7:20 a.m.