Preliminary information from an interview with Richard Vance, the pilot of the red Eurocopter AS350, suggests a passenger's harness somehow got wrapped around the fuel shut-off switch, accidentally cutting off the fuel supply to the helicopter and resulting in engine failure, multiple officials briefed on the investigation told ABC News.
Vance, 33, a pilot for Liberty Helicopter tours, radioed "Mayday! Mayday! Mayday!" just before 7 p.m. Sunday and reported "engine failure" just before the helicopter went down in the East River between East 86th and East 96th streets near Manhattan's Upper East Side.
The NYPD identified those killed in the crash as Daniel Thompson, 34, and Tristian Hill, 29, both of New York; Trevor Cadigan, 26, Brian McDaniel, 26, both of Dallas; and Carla Vallejos-Blanco, 29, of Argentina.
Cadigan, who has a degree in journalism from Southern Methodist University in Dallas, had recently moved to New York to begin a career with Business Insider, according to ABC station WFAA-TV in Dallas. Cadigan had been an intern at WFAA, where his father, Jerry Cadigan, works as a production manager.
"The entire WFAA family is heartbroken by the sudden and tragic loss of Trevor Cadigan," WFAA said in a statement. "We would like to thank the many friends and former employees of WFAA who have reached out to offer your condolences and support. Our thoughts and prayers are with all of Trevor's family and friends, and with the families of all of the victims of yesterdays' tragic accident."
McDaniel, 26, was a member of the Dallas Fire-Rescue, WFAA reported. He was on vacation in New York with a friend.
Vallejos-Blanco was visiting New York from her native Argentina, according to the Consulate General Argentina in New York.
In a statement released today, Liberty Helicopters said, "We are focused on supporting the families affected by this tragic accident and on fully cooperating with the FAA and the NTSB investigations. These agencies have asked us to respect the investigative process by referring all press inquiries to them for any further comment."
Vance, 33, was the only one to survive the crash in the frigid waters of the East River.
In two interviews with New York City police investigators, Vance said that when he first noticed he was having engine problems, he thought about landing in Central Park, but ruled that out and headed toward the East River, two officials briefed on the investigation told ABC News.
Vance told investigators he couldn't figure out what was wrong with the aircraft until he saw a tether from one of the passenger's harnesses strangling the fuel line, the officials said. By then, Vance had lost all power and prepared for a crash water landing.
He told investigators he attempted to inflate the emergency pontoons on the helicopter's skids prior to hitting the water, but the pontoons, which would have kept the aircraft afloat, did not inflate and the helicopter listed to one side and flipped over shortly after impact, officials said.
NTSB spokeswoman Bella Dinh-Zarr said at a press conference this afternoon that the crash occurred at 7:08 p.m. ET Sunday and her team "will be looking at other sister helicopters and see if this helicopter's harnesses were functioning and if the passengers were using them."
NTSB senior investigator Todd Gunther explained that while all of the helicopter's pontoons "had deployed" the critical issue is to determine "the sequence of events and did [the pontoons] deploy properly."
He also said the pontoons are required to be certified and maintained.
Officials said the passengers chartered the helicopter for a photo shoot and were tightly harnessed because the doors were left open so they could get better pictures.
Due to the doors being open, the helicopter quickly filled up with water and began to sink, officials said.
While Vance was able to immediately free himself from his harness, the passengers remained buckled in and trapped in the helicopter, which flipped over and submerged.
The helicopter drifted all the way down to E. 59th Street, where rescuers were finally able to reach it and free the trapped passengers by cutting their harnesses, according to FDNY Commissioner Daniel Nigro.
Earlier this afternoon investigators used a crane to lift the helicopter off the water from where it was moored overnight with flotation devices. The aircraft, which appeared to have a broken main rotor blade, was placed on a barge and carried away for inspection.
The NTSB's Dinh-Zarr said "it was legal" for the helicopter "to have the doors open."
The chopper is now at a secure site so she and her team can "figure out what happened."
According to FAA records, this was the third crash in New York for Liberty Helicopters in the past 11 years.
In August 2009, nine people, including the pilot, were killed when the one of the company's helicopters collided with a small private plane over the Hudson River. Investigators determined that the helicopter was flying too high when it made contact with the plane.
In 2007, a Liberty helicopter carrying eight people plummeted into the Hudson River. An off-duty paramedic was on board the aircraft and helped everyone escape without injury. The accident was caused by a malfunction in the main rotor blade of the helicopter, according to the FAA report.
ABC News' Mark Crudele and M.L. Nestel contributed to this report.