YONKERS, N.Y. - An engineer whose speeding commuter train ran off the rails along a curve, killing four people, nodded at the controls just before the wreck, and by the time he caught himself it was too late, a union official said Tuesday.

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," Bottalico said. "That is, you sometimes have a momentary nod or whatever that might be. How long that lasts, I can't answer that."

Rockefeller's attorney did not return calls. During a late-afternoon news conference, federal investigators said they were still talking to Rockefeller and did not comment on his level of alertness around the time of the Sunday morning wreck in the Bronx.

Separately, two law enforcement officials said the engineer told police at the scene that his mind was wandering before he realized the train was in trouble and by then it was too late to act. One official said Rockefeller described himself as being "in a daze" before the wreck.

The officials, who were briefed on the engineer's comments, were not authorized to discuss the investigation publicly.

Questions about Rockefeller's role mounted rapidly after investigators disclosed Monday that the Metro-North Railroad train jumped the tracks after going into a curve at 82 m.p.h., or nearly three times the 30 m.p.h. speed limit. The speed limit for the earlier section of straight track was 70 m.p.h. Dozens of people were hurt.

"He caught himself, but he caught himself too late," Bottalico said. ". . . He put the train in emergency, but that was six seconds prior to derailment."

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. He said investigators had found no problems with the brakes or signals.

Alcohol tests on crew members were negative, and investigators were awaiting results of drug tests, the NTSB official said.

On the day of the crash, Rockefeller, 46, was on the second day of a five-day workweek, reporting at 5:04 a.m. after a typical nine-hour shift the day before, Weener said.

"There's every indication that he would have had time to get full restorative sleep," Weener said.

Weener did not 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 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."

As Rockefeller stayed out of sight, his union and former coworkers spoke up in his defense.

"This is a man who is totally distraught by the loss of life, and he's having a tough time dealing with that," Bottalico said.

He added: "Once the NTSB is done with their investigation and Billy is finished with his interview, it will be quite evident that there was no criminal intent with the operation of his train."

Meanwhile, crews were rebuilding the damaged track. Officials expect 98 percent of service to be restored to the affected line Wednesday, Gov. Andrew Cuomo said.