Updated: March 12, 2018 5:30 PM ET | Originally published: March 12, 2018 8:33 AM EDT

A helicopter crashed into the East River in New York City on Sunday night, killing all five passengers aboard. The only survivor was the pilot.

All of the passengers had been strapped into their seats in tight harnesses, and the pilot was the only person able to free himself from the downed aircraft, according to officials of the Fire Department of New York.

The passengers were on a private charter for a photo shoot being run by Liberty Helicopter Tours, New York Police Commissioner James O’Neill at a news conference Sunday.

Here’s what we know about the fatal crash so far:

What Happened?

The aircraft went down shortly before 7 p.m. just south of 86th St. in the middle of the river near Roosevelt Island, O’Neill said.

A private tugboat was the first to arrive on the scene of the crash and assisted in the response. A search and rescue response began immediately. The NYPD, FDNY and the U.S. Coast Guard all responded to the incident.

An investigation into the deadly crash is being conducted the National Transportation Safety Board, said O’Neill. Todd Gunter, a senior aviation investigation at the NTSB, will lead the investigation. Officials said Tuesday would be the NTSB’s first full day on scene, and that the investigation would take five to seven days.

What Caused the Crash?

It is unclear exactly why the helicopter crashed, but NBC 4 New York reported that the pilot issued a distress call minutes before the crash, saying “Mayday…mayday…mayday…East River engine failure!”

The pilot, who NBC 4 New York identified as 33-year-old Richard Vance, said in a preliminary interview that a passenger’s harness may have wrapped around the fuel shut-off switch, cutting off fuel to the helicopter’s engine, multiple officials involved with the investigation said, according to ABC.

Witnesses who saw the helicopter plummet from the sky said it looked like it was “flying too fast and descending too quickly,” according to the New York Times. After hitting the water, the helicopter tipped over and flipped upside down, the witnesses described. One witness said they saw the pilot climb on the submerged helicopter and shout for help, the Times reported.

Who Was on Board the Helicopter Before It Crashed?

Along with the pilot, Vance, the five victims were identified by the NYPD. They are: 34-year-old Daniel Thompson and 29-year-old Tristan Hill, of New York, 26-year-olds Trevor Cadigan and Brian McDaniel, of Dallas, and 29-year-old Carla Vallejos-Blanco, of Argentina, the department confirmed to TIME.

Vance was taken to the hospital and released later Sunday night, New York Fire Commissioner Daniel Nigro said. At a press briefing Monday, a NTSB official said the board “will be asking him to be interviewed and we hope he will comply because obviously our only purpose here is to make sure this type of accident never happens again.”

“We will be looking into the pilot’s background but we don’t have any information on it yet,” the official added.

Officials said the passengers were on a sightseeing photoshoot and had taken off from Kearney, New Jersey.

Why Couldn’t Rescuers Save the Passengers?

“One of the most difficult parts of the operation…is the 5 people besides the pilot were all tightly harnessed,” Nigro said Sunday night. “So these harnesses had to be cut and removed to in order to get these folks off of this helicopter which was upside down at the time and completely submerged.”

Nigro said that three of the passengers were removed by divers from the helicopter in critical condition and taken to the hospital, where they did not survive, and two of the passengers were pronounced dead on the scene.

“It took a while for the divers to get these people out,” he said. “They worked very quickly, as fast as they could. That’s 50 ft. of water there, there was a 4 mile an hour current, the temperature was below 40s.”

At Monday’s press conference, NTSB officials said the helicopter was equipped with three floating devices, which did inflate, but still failed to keep the helicopter afloat, they said.

“We will be looking into the sequence of events and whether they were deployed properly,” Gunter said.

Contact us at letters@time.com.

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