He called Rockefeller "a guy with a stellar record who, I believe, did nothing wrong."
"You've got a good guy and an accident," he said. "A terrible accident is what it is."
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."
NTSB member Earl Weener said it was too soon to say whether the accident was caused by human error. But he said investigators have found no problems with the train's brakes or rail signals.
Alcohol tests on the train's crew members were negative, and investigators were awaiting the results of drug tests, the NTSB said.
Meanwhile, Joseph Szabo, head of the Federal Railroad Administration, said in a letter Tuesday that his administration and the U.S. Transportation Department "have serious concerns" following Sunday's accident and three others that occurred in New York and Connecticut from May through July.
Szabo noted that a federal team has been working closely with Metro-North Railroad and the Metropolitan Transportation Authority, but said "immediate corrective action is imperative."
The MTA said in a statement that it would work with federal agencies to improve safety, and was "conducting a comprehensive probe of the safety culture throughout the MTA."
Railroad employees were also getting expanded safety briefings.
Federal investigators wouldn't comment on Rockefeller's level of alertness around the time of the wreck. They said late Tuesday they had removed Bottalico's union, the Association of Commuter Rail Employees, as a participant in the investigation for publicly discussing confidential information.
Crews are rebuilding the damaged track where Rockefeller's train crashed. One of three Hudson Line tracks reopened Wednesday. Commuters said they were grateful service was restored fairly quickly.
"I know it was awful for the people who were hurt but it was awful for Metro-North too. Their tracks were torn up, they're going to get sued. I'm just so impressed that they're up and running," said rider Mark Marmer, 45, of the Bronx.
Passenger Matthew Adam, 37, lives close enough to the crash site that he heard it, but he said he too was pleased that service was restored, although, he said he had to reassure his 5-year-old that "daddy is still safe on the train."
Questions about Rockefeller's role mounted after investigators disclosed Monday that the train jumped the tracks after going into a curve at 82 mph, or nearly three times the 30 mph speed limit.
Rockefeller, 46, has worked for the railroad for 15 years and has been an engineer for 10, Weener said. He lives in Germantown, 40 miles south of Albany.
On the day of the crash, Rockefeller was on the second day of a five-day work week, and had reported 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," he said.
Weener said part of the investigation will be creating a 72-hour timeline of his activities.
Chartier said Rockefeller had gotten "a proper amount of sleep," having gone to bed at 8:30 the previous night to wake up at 3:30 a.m. for his shift. He said Rockefeller, before going to bed, had been spending time at home.
Rockefeller had begun running that route on Nov. 17, two weeks before the wreck. Bottalico said Rockefeller was familiar with the route and qualified to run it.
He said Rockefeller 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."
The New York Police Department is conducting its own investigation, with help from the Bronx district attorney's office, in the event the derailment becomes a criminal case.
Gov. Andrew Cuomo said Tuesday that 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," he said. "There's such a gross deviation from the norm."
A former supervisor, Michael McLendon, who retired from the railroad about a year ago, called Rockefeller "a stellar employee."
McLendon said he was stunned when he heard about the crash, shortly after opening his mail to find a Christmas card from Rockefeller and his wife.
"I said, 'Well, I can't imagine Billy making a mistake,'" McLendon said. "Not intentionally, by any stretch of the imagination."
University of Dayton professor Steven Harrod, who studies transportation, said trains typically don't have a speed or cruise control but a power control, and once it is set a train can 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.
In case of an engineer becoming incapacitated, the train's front car was equipped with a dead man's pedal, which must be depressed or the train will automatically slow down.
Trains also can have alarms, sometimes called alerters, which 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 train that derailed didn't have such a system, a Metro-North spokeswoman said.
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.
Peltz reported from New York. Associated Press writers Frank Eltman in Mineola; Michael Gormley in Albany; Michael Hill in Wappingers Falls; and Meghan Barr and Tom Hays in New York and researcher Rhonda Shafner contributed to this report.