The Metro-North Railroad train car that derailed Sunday morning was traveling at 82 mph when it rounded a sharp turn, which is nearly three times the permitted speed limit when rounding the turn, federal investigators said.

The throttle of the train car was still engaged, which gave the engine power, until it came to a stop around 7:20 a.m. EST after the train hurtled toward the Harlem River, killing four people and injuring more than 70.

The investigation is being led by the National Transportation Safety Board. Board member Earl Weener said the train's abrupt power shift came "very late in the game." The board said it is still unclear if the speed was the result of human error or malfunctioning equipment.

The discovery of the train's speed has put a focus on the engineer at the center of the investigation. The maximum allowable speed through the curve is 30 mph, and driving on straight track permits speeds no greater than 70 mph, The New York Times reports.

Investigators are looking into the possibility that the engineer, William Rockefeller, fell asleep, or that he was distracted. Keith Holloway, a spokesman for the board, said, "Part of our investigation, as in all investigations, is to look at human performance factors."

Rockefeller's cellphone was recovered, and results of drug and alcohol tests conducted after the crash are not yet known, according to The New York Daily News. 

Investigators said the train's brakes seemed to have been operating correctly.

"We are not aware of any problems or anomalies with the brakes," Weener said.

The tracks in the area are also reported to have been in good condition.

The safety board's interview with Rockefeller, a Metro-North employee who lives in Germantown, N.Y., will continue this week, officials said.

Anthony Bottalico, the acting director of the Association of Commuter Rail Employees, said the interview was put on hold because of "the trauma of the whole thing and the lack of sleep" for Rockefeller.

Detectives from New York City and the Metropolitan Transportation Authority police, with assistance from Bronx district attorney Robert T. Johnson, will investigate the derailment in addition to the safety board.

Bottalico conjectured that "when all is said and done here," the authorities would find there was "no criminal intent."

Rockefeller told emergency workers that he "dumped the brakes," which is an emergency maneuver, after he realized that the train was traveling too quickly.

Officials said an important question is why the train was traveling so fast in the first place.

Rockefeller, 45, is a veteran train engineer, and was not working overtime when conducting the train.