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Julio Cortez, Associated Press
Commuters walk near the light rail station at the Hoboken Terminal, Friday, Sept. 30, 2016, in Hoboken, N.J. Commuters are using alternative travel in and out of Hoboken a day after a commuter train crashed into the rail station, killing one person and injuring more than 100 people.

HOBOKEN, N.J. — Federal investigators trying to figure out the cause of the deadly rail crash at the Hoboken station hoped to question the engineer and lift clues Friday from the train's black box recorders, though one of the devices was proving difficult to extract from the mangled wreckage.

The devices contain information on speed, braking and other conditions that could help investigators determine why the NJ Transit commuter train smashed through a steel-and-concrete barrier and hurtled into the station waiting area Thursday morning. One person was killed and more than 100 others were injured.

National Transportation Safety Board investigators aimed to speak to engineer Thomas Gallagher, 48, on Friday. State officials said he was cooperating.

Gallagher, a NJ Transit engineer for about 18 years, was pulled from the wreckage, treated at a hospital and released.

Investigators were also examining the event recorder taken from the locomotive at the rear of the train, NTSB Vice Chairman T. Bella Dinh-Zarr said.

But officials said it was proving difficult to extract a recorder from the forward-facing camera in the train's badly mangled first car without damaging the device. That recorder should show what was ahead of the train before it crashed.

"The one thing we know for sure is that the train came into the station too fast. Why that is, we don't know," New Jersey Gov. Chris Christie said.

"Was it error by the engineer? Did he have some type of medical emergency or circumstance that rendered him unable to control the train? Was there some equipment failure that didn't allow him to slow down?"

Some witnesses said they didn't hear or feel the brakes being applied. Authorities would not estimate how fast the train was going before it hit the bumper at the end of its track. But the speed limit into the station is 10 mph.

Bumpers are meant mainly to denote the end of a track, not to stop a fast-moving train, said David B. Clarke, who runs the Center for Transportation Research at the University of Tennessee, Knoxville.

Some bumpers are designed to absorb the impact if a slow-moving car gets loose, but the maximum speed one can handle can be as low as 5 mph in some cases, he said.

Trains are supposed to stop well clear of bumpers, Clarke said.

Falling debris from the crash killed 34-year-old Fabiola Bittar de Kroon, who had just dropped her toddler daughter off at day care before rushing to catch a train. Sixteen of the injured remained hospitalized, two in intensive care.

More than 100,000 people use NJ Transit to commute from New Jersey to New York City each day. The NJ Transit portion of the Hoboken station remained closed Friday, slowing the morning commute.

The wreck has raised questions of whether technology called positive train control would have made a difference if NJ Transit had installed it. The GPS-based system is designed to prevent accidents by automatically slowing or stopping trains that are going too fast.

Railroads are under government orders to install positive train control by the end of 2018. The deadline has been repeatedly extended at the request of the railroad industry.

Sisak reported from Philadelphia. Associated Press writers David Porter, Dake Kang and Josh Cornfield in Hoboken; Megan Trimble in Philadelphia; Jennifer Peltz in New York; and Joan Lowy in Washington contributed to this report.