U.S. federal authorities were beginning an exhaustive investigation Monday into what caused a New York City commuter train to derail, killing four people and injuring more than 60 others.
The National Transportation Safety Board 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 inches from the water at a bend in the New York City borough of the Bronx, where the Hudson and Harlem rivers meet.
NTSB official Earl Weener says a second data recorder has been retrieved from the train involved in a fatal New York City derailment. Mr. Weener said Monday at the crash site that the recorder was found in the train's front car and has been sent to Washington for analysis.
The other event recorder was found earlier in the rear locomotive.
Weener said investigators hope to download information from the memory cards from that recorder on Monday. They hope it can provide information on the speed of the train, how the brakes were applied and the throttle setting.
He says they've already had some success in retrieving data. But the information has to be validated before it's made public.
The NTSB said it would consider whether excessive speed, mechanical problems or human error could have played a role in the Sunday morning crash, which threw some riders from toppling cars.
It was the latest accident in a troubled year for the second-biggest U.S. commuter railroad, which had never experienced a passenger death in an accident in its 31-year history.
Officials warned the 26,000 weekday riders of Metro-North railroad to brace for crowded trains during the morning commute.
The locomotive was hoisted back on the track before dawn Monday morning, and two cranes were in place to lift the rest of the toppled cars pending approval of the board, spokesman Aaron Donovan said.
About 150 people were on board when the train derailed as it rounded a riverside curb. Donovan said the railroad believed everyone aboard has been accounted for.
Some of the passengers on the Metro-North train from the town of Poughkeepsie to Manhattan were jolted from sleep around 7:20 a.m. to screams and the frightening sensation of their compartment rolling over on the bend.
When the motion stopped, all seven cars and the locomotive had lurched off the rails.
In their efforts to find passengers, rescuers shattered windows, searched nearby woods and waters and used pneumatic jacks and air bags to peer under wreckage.
NTSB board member Earl Weener said at a news conference Sunday the agency had just begun its investigation and hadn't yet spoken to the train's engineer, who was among the injured. Authorities did not release his name.
New York Gov. Andrew Cuomo said the track did not appear to be faulty, leaving speed as a possible culprit for the crash. The speed limit on the curve is 30 mph (48 kph), compared with 70 mph (113 kph) in the area approaching it, Weener said.
Authorities did not yet know how fast the train was traveling but had found a data recorder, he said.
Authorities identified the victims Sunday as Donna L. Smith, 54; James G. Lovell, 58; James M. Ferrari, 59; and Ahn Kisook, 35. Three of the dead were found outside the train, and one was found inside, authorities said.
Lovell, an audio technician, was traveling to midtown Manhattan to work on the famed Rockefeller Center Christmas tree, said longtime friend Janet Barton. The tree-lighting ceremony is Wednesday night.
"The 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.
Eleven of the injured were believed to be critically wounded and another six seriously hurt, according to the Fire Department. After visiting an area hospital Sunday evening, New York City Mayor Michael Bloomberg told reporters that the 11 who originally were critical no longer appeared to have life-threatening injuries.
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.
Sunday's accident came six months after an eastbound train derailed in Bridgeport, Connecticut, 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.
For decades, the NTSB has been urging railroads to install technology that can stop derailing caused by excessive speed, along with other problems.
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 percent 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.
Associated Press writers Kiley Armstrong, Colleen Long, Jake Pearson and Jennifer Peltz in New York, Joan Lowy in Washington and Stephen Singer in Hartford, Conn., contributed to this report.
Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.