A commuter train that derailed over the weekend, killing four passengers, was hurtling at 132 km/h as it entered a 50 km/h curve, a federal investigator said Monday. But whether the wreck was the result of human error or brake trouble was unclear, he said.

Asked why the train was going so fast, National Transportation Safety Board member Earl Weener said: "That's the question we need to answer."

He would not disclose what the engineer operating the train had told investigators. Weener said investigators were examining the engineer's cellphone — apparently to determine whether he was distracted.

Weener said the information on the locomotive's speed was preliminary and extracted from the Metro-North train's two data recorders, taken from the wreckage after the Sunday morning accident in the Bronx.

He said the throttle went to idle six seconds before the derailed train came to a complete stop — "very late in the game" for a train going that fast — and the brakes were fully engaged five seconds before the train stopped.

Asked whether the tragedy was the result of human error or faulty brakes, Weener said: "The answer is, at this point in time, we can't tell."

He said investigators are not aware of any problems with the brakes during the nine stops the train made before the derailment.

Meanwhile, the engine of the commuter train is upright again, railway officials said.

Metro-North spokesman Aaron Donovan told The Associated Press that cranes re-railed the engine at 4:20 a.m. ET Monday.

Two cranes are in place to lift the rest of the derailed cars, pending approval from the U.S. National Transportation and Safety Board. Federal investigators are at the site, CBS News reporter Marlie Hall told CBC News Network from the scene Monday morning.

"They are poring over the wreckage, trying to determine what led to that deadly derailment," she said.

Donovan said about 150 people were aboard when the train derailed as it rounded a riverside curve in the Bronx. More than 60 people were injured. All passengers have been accounted for.

NYC Train Derailment

An Amtrak train, top, travelling on an unaffected track, passes a derailed Metro North commuter train Sunday in the Bronx borough of New York. Officials are standing on a curve in the tracks where the Metro North train derailed. (Mark Lennihan/AP Photo)

The accident occurred on the Hudson line, which carries 26,000 weekday riders. The commute was expected to be slower Monday.

"Train officials are making shuttle buses available to commuters," Hall said. "But they are encouraging anyone that can telecommute to work from home."

The NTSB said its investigators could spend up to 10 days probing all aspects of the accident that toppled seven cars and the locomotive, leaving the lead car only centimetres from the water at a bend in the Bronx where the Hudson and Harlem rivers meet.

It was the latest mishap in a troubled year for Metro-North, which had never before experienced a passenger death during an accident in its 31-year history.

Victims named

As deadly as the derailment was, the toll could have been far greater had it happened on a weekday, or had the lead car plunged into the water. The train was about half-full at the time of the crash, rail officials said. 

The MTA identified the victims as Donna L. Smith, 54, of Newburgh; James G. Lovell, 58, of Cold Spring; James M. Ferrari, 59, of Montrose; and Ahn Kisook, 35, of Queens. Three of the dead were found outside the train, and one was found inside, authorities said. Autopsies were scheduled for Monday, the New York City medical examiner's office said.

Lovell, an audio technician, was travelling from his Cold Spring home to midtown Manhattan to work on the famed Rockefeller Center Christmas tree, longtime friend Janet Barton said. The tree-lighting ceremony is Wednesday night.

NBC's Today show expressed condolences to the family of Lovell, a married father of four who had worked on the program and other NBC shows. "He always had a smile on his face and was quick to share a friendly greeting," Today executive producer Don Nash said in a message to staff.

For decades, the NTSB has been urging railroads to install technology that can stop derailing caused by excessive speed, along with other problems.

New technology

A rail-safety law passed by Congress in 2008 gave commuter and freight railroads until the end of 2015 to install the systems, known as positive train control. PTC is aimed at preventing human error — the cause of about 40 per cent of train accidents. But the systems are expensive and complicated. Railroads are trying to push back the installation deadline another five to seven years.

Metro-North is in the process of installing the technology. It now has what's called an "automatic train control" signal system, which automatically applies the brakes if an engineer fails to respond to an alert that indicates excessive speed.

Such systems can slow trains in some circumstances but not bring them to a halt, said Grady Cothen, a former Federal Railroad Administration safety official.

Sunday's accident came six months after an eastbound train derailed in Bridgeport, Conn., and was struck by a westbound train. The crash injured 73 passengers, two engineers and a conductor. In July, a freight train full of garbage derailed on the same Metro-North line near the site of Sunday's wreckage.

With files from CBC News