New York Governor Andrew Cuomo said Monday that a train that derailed in a devastating accident that killed four passengers and wounded 67 others was probably traveling too fast.
There are three possibilities behind Sunday's crash, which struck during America's post-Thanksgiving shopping frenzy, Cuomo said: "Problem with the track, equipment problem or operator error."
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"Working with the experts over the past day, I think it is going to be speed-related," he told NBC, adding that the sharp curve where the train veered off the tracks was not enough to explain the accident.
"This was a tricky turn on the system, but it's a turn that's been here for decades and trains negotiate all day long," he said.
"I think it's going to turn out to be about the speed more than anything, and the operator's operation of the train at that time."
After retrieving the train's two "black boxes" -- one from the front and one from the rear -- investigators from the National Transportation Safety Bureau were continuing their probe at the scene, in the Bronx borough north of Manhattan.
The train, carrying between 100 and 150 people, crashed at around 7:20 a.m. Sunday as it headed south to Grand Central Station in Manhattan.
The train's seven cars derailed just before it reached Spuyten Duyvil station and flew across a grassy bank separating the railroad from the Hudson and Harlem rivers, which meet at that point.
The front car came to rest only a few feet from the water, and two cars toppled on their side.
Speaking on CNN, Cuomo described the horror the passengers experienced as the train skidded at high speed.
"The windows broke out, the doors opened and they were picking up stones, rock, dirt, tree limbs were flying through the cars," he said.
Some passengers were "impaled" by debris as train cars flew into the air, officials have said, while others had to be cut free from tangled metal.
The Metropolitan Transportation Authority identified the four victims, who ranged in age from 35 to 59. Two were men, two were women, and all were New York-area residents.
Three of the victims had been thrown from the train.
The New York Fire Department said 11 other people were seriously hurt, and another 56 suffered minor injuries.
As trains reach the sharp curve north of Spuyten Duyvil station, they are meant to slow down from 70 miles and hour to 30 miles an hour, Cuomo said.
However, several passengers have said the train was going too fast as it approached the turn.
"Our mission is to understand not just what happened, but why it happened, with the intent of preventing it from happening again," Earl Weener, a National Transportation Safety Board official, told reporters Sunday.
Commuter rail service in the area around the accident remained suspended Monday.