Three of the four people killed were found outside of the train after the 7:20 a.m. crash, apparently thrown from the train as it derailed, sources said.
The four people killed in the crash were identified by the MTA: Ahn Kisook, 35, of Queens; Donna Smith, 54, of Newburgh; James Lovell, 58, of Cold Spring; and, James Ferrari, 59, of Montrose.
More than 60 people — including the train's operator — were injured in the crash, sources said. None of the critically hurt passengers appear to have life-threatening injuries. With the Thanksgiving holiday weekend coming to an end, there were more than 100 passengers on the train, which is higher than usual for a Sunday, according to the MTA.
"I thought I was going to die," said train passenger Alex Marquez, speaking to CBS News. "It was a loud crash and everything, I didn’t think we were going to survive."
The National Transportation and Safety Board was on scene, and investigators were looking at several possible factors that might have caused the crash, including mechanical problems, track or signal issues and human error.
Sources said the train's operator, a 20-year veteran of Metro-North, told investigators that he had tried to slow the train down, but that the brakes hadn't worked. His account had not been confirmed.
Metro-North trains can be traveling at up to 75 mph before they are supposed to slow down to roughly 30 mph once they reach a curve in the tracks where the Hudson River meets the Harlem River, NTSB member Earl Weener told reporters. The curve has a 30 mph speed limit, officials said.
Witnesses and passengers reported feeling the train had lost control at one point.
As the train's cars slid along the ground, rocks and sticks were sucked inside the cars where they became projectiles, officials said. The lead car came to rest at the water's edge of the Harlem River. The second and third cars flipped onto their sides.
"We were leveling out all the trees and debris over here," a passenger who was in the front car told CBS. “Everybody on the train got thrown to one side. You could hear and feel the trains flipping behind us.
"I saw a woman get thrown out of the window, and she died right in front of me."
The Hudson Line train left Poughkeepsie at 5:54 a.m. headed for Grand Central Terminal, with seven cars pushed from behind by a diesel locomotive. All seven cars derailed at a curved portion of the trackbed 100 yards north of the Spuyten Duyvil station.
Firefighters had to stabilize the train with airbags and hydraulic jacks, and use metal cutters to rescue passengers, sources said. Divers in wetsuits scoured the nearby waterway until all passengers were accounted for, sources said.
Gov. Andrew Cuomo said the train's "black box" would reveal whether the brakes had been hit manually, or if the train had been speeding.
Officials said the black box had been recovered, and that data was already being analyzed on Sunday evening.
In addition to the operator, the train had three conductors in its crew.
This is not the first time a train has derailed near Spuyten Duyvil.
In July, a northbound freight train hauling garbage also derailed on the same Metro-North tracks between the Spuyten Duyvil and Marble Hill stations. Ten cars of a 24-car train jumped the tracks, halting weekday service along the line. No passengers were injured at the time.
"We'll be looking at that," said Weener, when asked by reporters if it was believed the incidents could be related, "but at this point we have no indication there was a connection."
Metro-North service between Tarrytown and Grand Central was suspended, the MTA said. Shuttle buses were available to take passengers to the White Plains station along the Harlem Line for service into Manhattan. Amtrak had temporarily halted Empire Line service between Manhattan and Albany, but it was restored by Sunday afternoon.
Injured passengers were taken to nearby hospitals, including Jacobi, Montefiore, Columbia Presbyterian, Elmhurst, Lincoln and St. Barnabas.
A family center was set up at JFK High School, at 99 Terrace View Ave. in the Bronx, and the MTA encouraged family members to call (718) 817-7444 or (212) 639-9675 for information on the status of relatives on board.
With additional reporting by Bruce Katz.