The series of still photographs taken from surveillance camera video shows the fuselage, containing the engine and rotors, separating from the helicopter’s tail. The rotor blades and the transmission then detach from the cabin that’s carrying the passengers and the pilot.

The images were included in the preliminary report about the flight released by the National Transportation Safety Board.

“Several witnesses described hearing several loud ‘bangs’ emanating from the helicopter before it broke up and descended into the river,” the report says.

Justin Green, an aviation lawyer and former Marine helicopter pilot, said the sequence of images shows the helicopter yawing severely and the tail boom failing, suggesting it was most likely struck by the aircraft’s main rotor blades during flight.