All five passengers aboard a tour helicopter died when the aircraft crashed into the East River Sunday evening, authorities said, marking one of the worst civilian aviation fatalities of any kind in the United States in the last few years. The pilot of the helicopter, who managed to escape the overturned chopper , was the only survivor. Law enforcement sources identified him as Richard Vance, 33. A senior law enforcement official tells News 4 that Vance speculated in an initial interview it was possible one of the passengers inadvertently hit the fuel cut-off switch with a piece of equipment, which may have caused the engine to sputter and the chopper to plunge into the river. Former Md. Confederate Site Rededicated to Harriet Tubman The five passengers became trapped in the inverted aircraft and had to be pulled from frigid waters by divers, officials said. Three of them were taken to area hospitals in critical condition and died early Monday, while the other two were pronounced dead at the scene. Sources indicated the dead were four men and one women, though identities were not immediately available. Law enforcement sources said Vance was released from the hospital at some point overnight. Details on the nature of his injuries weren't known. Man Gets 30 Years for Shaking Baby, Causing Brain Damage At a press conference Sunday night, FDNY Commissioner Daniel Nigro said the pilot was able to free himself and was taken by a fire boat to shore. Nigro described the pilot as being OK. He said he was taken to Cornell Medical Center, where he remained early Monday. "It's a great tragedy that we had occur here on an otherwise quiet Sunday evening," Nigro said. Fla. Governor Signs Gun Restrictions; NRA Sues The helicopter went down in the waters near East 86th Street and the FDR Drive shortly after 7 p.m., according to officials, who said police received dozens of 911 calls in the minutes after the crash. "Mayday... Mayday... Mayday... East River engine failure!" the pilot said during a distress call moments before losing control of the helicopter and plummeting into the water. Witnesses said the pilot was waving with both arms and yelling "Help!" from the water. A Long Island woman having dinner with her sister and brother-in-law at their apartment near 92nd Street captured the exact moment of the crash on video . "It was unbelievable to watch because you don't believe it is actually going to hit it and then the next thing you know, it's hitting the water," Arineh Nazarian said. Her video shows the chopper hovering in the air, then suddenly descend toward the river, where it crashes, its half-submerged propellers madly spraying water. It overturns, then sinks. Other videos show emergency responders rushing to the water as crowds of onlookers gather at the shore. Officials said the helicopter, owned by Liberty Helicopter Tours, was a private charter out for a photo shoot. The company has not commented on the crash. Chopper 4 reporter Kai Simonsen says passengers on such flights are usually strapped in as they take photos of the city. The passengers are normally shown a safety video before going up that instructs them to use a cutter on their harness to break free during an emergency, Simonsen says. But after FDNY and NYPD harbor and aviation units descended on the crash site, divers discovered the five passengers still strapped into their harnesses inside the submerged helicopter. Nigro said the East River had currents of 5 mph and waters below 40 degrees at the time. "The five people besides the pilot were all tightly harnessed, so these harnesses had to be cut and removed in order to get these folks off this helicopter, which was upside down at the time and completely submerged," Nigro said. The Coast Guard and a private tugboat also assisted in the rescue, according to NYPD Commissioner James O'Neill, who said the tugboat crew were the first to arrive after the crash. The helicopter was recovered and towed to 23rd Street and the FDR Drive, where it was still submerged around midnight. The crash happened right in front of Gracie Mansion, the official residence of Mayor de Blasio, who was out of town this weekend. In a statement earlier Sunday evening, Gov. Cuomo said he was monitoring the situation. "Our thoughts and hope for safe recovery are with those who were aboard. We are thankful for our first responders at the scene," Cuomo said. The FAA said in a statement that a Eurocopter AS350 went down in the East River near the northern end of Roosevelt Island. The agency said the National Transportation Safety Board will lead the investigation in determining what caused the crash. The NTSB asked for any witnesses to come forward. The Aviation Safety Network, which tracks flight accidents and fatalities, had recorded at least 11 other fatal crashes worldwide involving AS350 variants over the last 18 months alone. According to that same database, Sunday's crash is likely the biggest U.S. civil aviation fatality since a Dec. 2016 Cessna crash in Ohio. Though chopper crashes in the East and Hudson rivers aren't necessarily uncommon, Sunday's crash has become one of the deadliest in the city's history. Photo Credit: @JJmagers/Twitter/Aaron Brown This story uses functionality that may not work in our app. Click here to open the story in your web browser.