The engineer whose speeding New York commuter train ran off the rails along a curve, killing four people, nodded off at the controls, and by the time he caught himself it was too late, a union official says.
William Rockefeller ''basically nodded,'' said Anthony Bottalico, leader of the rail employees union, relating what he said the engineer told him.
''He had the equivalent of what we all have when we drive a car. That is, you sometimes have a momentary nod or whatever that might be. How long that lasts, I can't answer that.''
During a late-afternoon news conference, federal investigators said they were still talking to Rockefeller, and they would not comment on his level of alertness around the time of the crash in the Bronx.
Separately, however, two law enforcement officials said the engineer told police at the scene that his mind was wandering before he realised the train was in trouble, and by then it was too late to do anything about it.
One of the officials said Rockefeller described himself as being ''in a daze'' before the wreck.
The officials, who were briefed on the engineer's comments, weren't authorised to discuss the investigation publicly and spoke on condition of anonymity.
Questions about Rockefeller's role mounted rapidly after investigators disclosed that the Metro-North Railroad train jumped the tracks after going into a curve at 132kmh, or nearly three times the 30miles per hour (48kmh) speed limit. In addition to the four people killed, dozens were hurt.
''He caught himself, but he caught himself too late. He powered down, he put the train in emergency, but that was six seconds prior to derailment,'' Bottalico said.
Rockefeller, who was operating the train from the front car, was treated at a hospital for minor injuries and released.
National Transportation Safety Board member Earl Weener repeated that it was too soon to say whether the accident was caused by human error. But he said investigators have found no problems so far with the brakes or signals.
Alcohol tests on the train's crew members were negative and investigators were still awaiting the results of drug tests, the NTSB official said.
On the day of the crash, Rockefeller was on the second day of a five-day work week, reporting at 5.04am Sunday (local time) after a typical nine-hour shift the day before, according to Weener.
''There's every indication that he would have had time to get full restorative sleep,'' Weener said.
Weener didn't address specifically what the engineer was doing in the hours before his shift started, but said part of the investigation would be creating a 72-hour timeline of his activities.
Bottalico said Rockefeller ''never said anything about not getting enough sleep''.
But he said the engineer had switched just weeks earlier from the night shift to the day shift, ''so he did have a change in his hours and his circadian rhythms with regard to sleep''.
Governor Andrew Cuomo said today the engineer could be faulted for the train's speed if nothing else.
''Certainly, we want to make sure that that operator is disciplined in an appropriate way. There's such a gross deviation from the norm,'' he said.
Steven Harrod, a University of Dayton professor who studies transportation, said that trains typically did not have a speed or cruise control, but a power control, and once it was set, a train could pick up speed on its own because of the terrain.
''Thus, if the engineer loses attention, the train can gain speed without intervention,'' Harrod said.
''The power control could have been set'' as the train left a station, ''and then forgotten by the engineer.''
In case of an engineer becoming incapacitated, the train's front car was equipped with a ''dead man's pedal'' that must be depressed or else the train will automatically slow down.
Trains also can have alarms, sometimes called ''alerters,'' that sound if the operators' controls haven't been moved within a certain timeframe.
If an engineer doesn't respond, often by pressing a button, brakes automatically operate. But the Metro-North train that derailed didn't have such a system, according to Marjorie Anders, a spokeswoman for Metro-North's parent, the Metropolitan Transportation Authority.
Regardless, ''neither of those two methodologies is truly a fail-safe approach,'' said Grady Cothen, a former Federal Railroad Administration safety official.
Congress has ordered commuter and freight railroads to install technology called positive train control - which uses electronics to monitor trains' positions and speed and stop derailments and other problems - by the end of 2015.
Rockefeller, 46 and married with no children, has worked for the railroad for 15 years and has been an engineer for 10, according to Weener.