The plot thickens and is deeply disturbing….One of the pilots on the Germanwings flight that crashed March 24, killing 150, was locked out of the cockpit before the crash, The New York Times reports, citing a senior military official involved in the investigation.

Audio from the cockpit voice recorder tells a chilling tale:

“The guy outside is knocking lightly on the door and there is no answer,” the official told the New York Times. “And then he hits the door stronger and no answer. There is never an answer.”

The pilot outside the cockpit is then heard trying to break the door down. At the very end of the flight, the official said, investigators are certain that the other pilot is “alone and does not open the door.”

Officials investigating the crash have not ruled out terrorism. The remote location of the crash, in the French Alps, has made the site difficult to reach and complicated the investigation.

This video show how a pilot might have been locked outside the cockpit of Germanwings 9525.