One of the pilots on the German plane that crashed in the French Alps, killing all 150 people onboard, left the cockpit and was unable to return before the plane went down, the New York Times reported on Wednesday, citing evidence from a cockpit voice recorder.

"The guy outside is knocking lightly on the door and there is no answer," an unnamed investigator told the Times. "And then he hits the door stronger and no answer."

"There is never an answer. You can hear he is trying to smash the door down," the investigator added.

NBC News has not confirmed the NY Times report. Earlier Wednesday, Remy Jouty, director of France's aviation investigation agency, told reporters that it was too soon to draw conclusions about why the plane went down on a routine flight from Barcelona to Dusseldorf, Germany.