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 New York 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.
"We just succeeded in getting an audio file which contains usable sounds and voices," he said. "We hope to have a first rough idea in a matter of days, and having a full understanding ... will take weeks and even months."
He said that there was no midair explosion, and that the plane "flew to its end." But he said investigators do not have a hypothesis on why the plane, Germanwings Flight 9525, began its eight-minute descent from cruising altitude and crashed.
The crash left remnants of the plane scattered all over the mountainside. The remote, rugged terrain has posed an enormous challenge for investigators.
"It's very difficult to see this because there's a lot of little pieces," Xavier Roy, the French civil aviation coordinator, told NBC News in an interview. "We cannot find a cockpit or big pieces, so it's very difficult to see."
Among the dead were at least three Americans. NBC News confirmed that Yvonne Selke and her daughter Emily, from Virginia, were killed in the crash. The State Department said later that a third American, whom it did not identify, was also killed.
The New York Times quoted a senior military official involved in the investigation as saying the cockpit audio showed "very smooth, very cool" conversation between the pilots in the early part of the flight.
The audio then indicated one of the pilots left the cockpit.
"We don’t know yet the reason why one of the guys went out,” the official added. "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 international police organization Interpol said Wednesday it is sending a team to assist with the identification of victims.