This story originally appeared on New York magazine:

New York has obtained a confidential document from the Malaysian police investigation into the disappearance of Malaysia Airlines Flight 370 that shows that the plane’s captain, Zaharie Ahmad Shah, conducted a simulated flight deep into the remote southern Indian Ocean less than a month before the plane vanished under uncannily similar circumstances.

The revelation, which Malaysia withheld from a lengthy public report on the investigation, is the strongest evidence yet that Zaharie made off with the plane in a premeditated act of mass murder-suicide.

The document presents the findings of the Malaysian police’s investigation into Zaharie. It reveals that after the plane disappeared in March of 2014, Malaysia turned over to the FBI hard drives that Zaharie used to record sessions on an elaborate home-built flight simulator. The FBI was able to recover six deleted data points that had been stored by the Microsoft Flight Simulator X program in the weeks before MH370 disappeared, according to the document. Each point records the airplane’s altitude, speed, direction of flight, and other key parameters at a given moment.

Read the full story at NY Mag.