A National Transportation Safety Board (NTSB) go-team is in New York City today, combing through the wreckage of a passenger train that derailed Sunday morning, killing four people and injuring more than 60.

The incident occurred at 7:20 a.m. as the seven-car Metro North train navigated a sharp curve in the Bronx.

New York Gov. Andrew Cuomo speculated that speed was the cause of the accident. The train derailed occurred in a 30-mph speed zone that was preceded by a 70 mph limit area. Cuomo said the investigation could take up to ten days.

The NTSB team consists of investigative specialists in track, signals, mechanical systems, operations, human performance, survival factors and recorders. Specialists from the NTSB Office of Transportation Disaster Assistance are also responding to the scene.

Investigators have recovered the black box data recorder from the crash site and will use it to help determine the accident cause.

The train’s engineer, who suffered minor injuries, has two decades’ experience with Metro North.

First responders said nearly a dozen of those injured were critical. Some of the victims were thrown from the train. The train held approximately 150 passengers – about half full.

Fire Commissioner Salvatore Joseph Cassano said that if the derailment had occurred on a weekday, with more passengers, it would have been “a tremendous disaster.”