Investigators searching for the cause of a New York commuter train derailment that killed at least four and injured more than 60 people have recovered both black boxes from the train.
The black boxes, also known as event data recorders, will provide information on whether speed, mechanical problems or human error may have caused the Metro-North to derail as it rounded a riverside curve in the Bronx borough of New York City Sunday morning. The event data recorders were said to be in good condition.
"We have recovered the event recorder of the cab car. We have downloaded the data off the locomotive. We've not had a chance to analyze it," National Transportation Safety Board member Earl Weener said Sunday evening. Weener says investigators will know today how fast the train was going, whether the brakes were applied and whether they worked.
Pictures From Fatal Train Crash in NYC
The train's operator reportedly told emergency workers the brakes failed, which is one possibility investigators are looking as the cause of the derailment, officials briefed on the investigation told ABC News.
Investigators have not said why the train derailed but the NTSB could speak to the train operator as soon as today.
Investigators will also examine the track's condition although New York Gov. Andrew Cuomo said Sunday the track did not appear to be faulty, leaving speed as a possible cause for the crash.
"Our mission is to understand not just what happened but why it happened with the intent of preventing it from happening again," Weener said.
NTSB officials worked overnight collecting evidence and spotlights were brought in to illuminate the mangled train. With the help of cranes, some of the train cars were lifted upright early this morning. NTSB officials said they expected to be on the scene investigating for a week to 10 days.
The dead were identified as Donna L. Smith, 54, of Newburgh, N.Y.; James G. Lovell, 58, of Cold Spring, N.Y.; James M. Ferrari, 59, of Montrose, N.Y.; and Ahn Kisook, 35, of Queens, N.Y.
Three of the dead were found outside the train, and one was found inside, authorities said. Autopsies were scheduled for later today, said the New York City medical examiner's office.
Lovell, an audio technician married with four children, was traveling from his Cold Spring home to midtown Manhattan to work on the famed Rockefeller Center Christmas tree, a neighbor told ABC News station WABC-TV.
Eleven people were in critical condition at area hospitals, according to Cuomo as of Sunday, although he said he believed they were in stable condition.
With the track out of commission for the next few days, thousands of people braced for a complicated morning commute today on the Hudson Line, with shuttle buses ferrying passengers to another line.
It's the second commuter train accident on the Metro-North line since July, but New York Police Commissioner Raymond Kelly told ABC News riders shouldn't worry.
"The systems are safe. Just based on sheer volume, sometimes accidents happen, but in terms of the specific cause here, that's going to have to be determined by a full investigation by the NTSB," he said.
The train, which was estimated to have had around 150 passengers on board, left Poughkeepsie for New York's Grand Central Terminal at 5:54 a.m. when it derailed at 7:20 a.m. along the sharp curve near the Spuyten Duyvil Station. The speed limit on the curve is 30 mph, compared with 70 mph in the area approaching it, Weener said.
At least two of the cars had flipped on their side after the crash, and one car stopped only feet from the banks of the Harlem River. Cuomo told reporters that the four fatalities were from the two cars that had flipped on their side. Firefighters, rescue workers and ambulances responded quickly to the scene, and some firefighters broke through windows to remove passengers from the train.
Some of the passengers were jolted from their sleep to screams and the frightening sensation of the train car rolling over.
"It was the speed of the car when I woke up and felt it tilting a bit and by the time I realized what was going on, everyone was getting thrown around," passenger Ryan Kelly told ABC News.
Kelly survived the crash but suffered a fractured hand.
"Everyone in my car was alright except for one woman who was pinned between two seats," he added.
ABC News' Aaron Katersky, Matt Hosford, Howard Price and Gio Benitez contributed to this report.