The China Eastern Airlines plane that crashed into a hillside in 2022, killing all 132 people on board, had its fuel supply cut mid-flight, newly released investigative material shows, which bolsters the theory that the aircraft was intentionally brought down.

While China still has yet to release a final report on the accident, findings released by the US National Transportation Safety Board this month show that levers controlling the flow of fuel to the jet’s engines were switched to the “cut-off” position while the Boeing 737 aircraft was at a cruising altitude of 29,000ft. The movement would have immediately cut off fuel supply to the engines, forcing them to shut down.

“Engine speeds decreased after the fuel switch movement,” the NTSB, which supported Chinese authorities’ in the crash investigation, said in the 2022 report, which was released on May 1 under the Freedom of Information Act.

Bloomberg News and other media outlets have previously reported preliminary evidence pointed to a murder-suicide event but no official information has previously been disclosed into the possible causes.

Chinese authorities have reportedly cited national security reasons for not releasing a final report. The Civil Aviation Administration of China did not respond to an email seeking comment. Boeing did not immediately reply to a request for comment.

Neil Campbell, a former air safety investigator at the Australian Transport Safety Bureau who worked on the 2018 Boeing 737 Max crash in Indonesia, said it is routine for jet fuel switches to be turned off after the plane has landed but almost never in flight, adding that the actions looked like a “deliberate event”.