One of the two pilots of the crashed Germanwings flight may have been locked out of the cockpit before the plane crashed in the French Alps, the New York Times reported.

The report quoted a senior military official involved in the investigation as saying that evidence from a cockpit voice recorder indicated that the pilot left the cockpit and could not re-enter, Xinhua reported .

“The guy outside is knocking lightly on the door and there is no answer, and then he hits the door stronger and no answer. There is never an answer, and you can hear he is trying to smash the door down,” the investigator said.

The investigator said: “We don’ t know yet the reason why the pilot went out, but what is sure is that at the very end of the flight, the other pilot is alone and does not open the door.”

The Airbus A320 aircraft, operated by Lufthansa’s budget airline Germanwings, crashed on Tuesday in southern France while flying from Spain’s Barcelona to Germany’s Duesseldorf.

There were no survivors among the 144 passengers and six crew members on board.