Helicopter taking off from NYC Pier 6 An unrelated helicopter on the helipad in Lower Manhattan in New York, on East River, Pier 6. (Photo: Shutterstock)

(Bloomberg) – The five passengers trapped in a helicopter that ditched into the East River off New York Sunday night may have died because they were wearing hard-to-remove harnesses in the stricken craft, investigators said.

Photography harnesses

The harnesses, which are different than traditional aircraft seat belts, are designed to allow people to safely photograph from a helicopter with the doors open. They attach from the rear and would be difficult to remove in an emergency, according to a passenger on another flight who said he photographed the helicopter before the crash.

Divers in fast-moving, frigid waters had to cut the people loose 50 feet below the surface in order to remove them, New York Fire Department Commissioner Daniel Nigro said.

"It took a while for the divers to get these people out," Nigro said at a briefing.

Mayday: 'Engine failure'

The Airbus SE AS350 helicopter, owned by Liberty Helicopters, went down shortly after 7 p.m. near East 86th Street as the pilot declared an emergency. The pilot was able to escape as the craft sank and was rescued.

"Mayday, mayday, mayday," the pilot told air traffic controllers as it was going down, according to a recording of the radio call. "East River. Engine Failure."

Emergency fuel shutoff may have been accidently switched

The pilot has told investigators that he suspects a bag owned by one of the passengers may have switched an emergency shutoff valve for fuel to the engines, CNN and ABC News reported.

The National Transportation Safety Board, which sent a team of 15 to investigate the accident, hasn't confirmed the report.

The helicopter is being towed to an unspecified secure facility so it can be examined, the NTSB said Monday in a tweet.

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