UPDATE | Death toll climbs to 7 in Amtrak train wreck

PHILADELPHIA (AP) — The death toll climbed to seven with the discovery of another body in the wreckage today as investigators tried to determine why an Amtrak train hurtled off the tracks while rounding a sharp curve.

More than 200 people were injured in the wreck that plunged screaming passengers into darkness and chaos Tuesday night.

Investigators recovered the locomotive's black box data recorders and said they expected them to yield crucial information, including how fast the train was going when it derailed in an old industrial neighborhood not far from the Delaware River shortly after 9 p.m.

"It's a devastating scene. There are many first responders out there. They are working. They are examining the equipment, seeing if there are any more people in the rail cars," Robert Sumwalt of the National Transportation Safety Board said.

Mayor Michael Nutter said some people remained unaccounted for, though he cautioned that some passengers listed on the Amtrak manifest might not have boarded the train, while others might not have checked in with authorities.

The dead included an employee of The Associated Press and a midshipman at the U.S. Naval Academy.