A newspaper is reporting that the voice recorder indicates that one of the pilots was locked out of the cockpit before a Germanwings jetliner plummeted into a remote Alpine mountainside.

The New York Times is citing an investigator it doesn’t identify as saying that the audio shows that after an ordinary start to the flight, one of the pilots left the cockpit and could not get back in.

The investigator told the newspaper that the pilot began knocking quietly on the door, then became more insistent, saying that eventually: “You can hear he is trying to smash the door down.”

The investigator does not speculate as to why the other pilot didn’t open the door or make contact with ground control before the plane crashed Tuesday, but the new evidence would be consistent with a terrorist attack.

All 150 people aboard were killed.

Earlier on Wednesday, the director of France’s aviation investigative agency said there currently is not the “slightest explanation” for what caused the Germanwings plane to lose altitude and crash in the Alps.

Remi Jouty says the investigation could take weeks or even months.

Jouty says the plane was flying “until the end” — slamming into the mountain, not breaking up in the air.

He says the final communication from the plane was a routine message about permission to continue on its route.  

Jouty confirmed that audio has been recovered from the cockpit recorder salvaged from the crash site. Jouty says the material includes sound and voices, and was extracted Wednesday afternoon from the mangled black box recovered from a mountainside.

Jouty says it was too early to draw conclusions from the recording. The case of the second black box, the flight data recorder, has been found, but not its contents, French President Francois Hollande said minutes earlier.

Jouty says he couldn’t confirm that the case of the second black box had been recovered. 

The U.S. State Department says a third American has been identified as a victim of the plane crash in France that killed a total of 150 people. 

It was earlier confirmed that American Yvonne Selke and her daughter Emily Selke were among the victims. 

Meanwhile, a bus with 14 relatives of the Spanish victims who died in the crash has left Barcelona for an overnight journey that will take them to the crash area by Thursday.Spain’s government has said at least 51 Spaniards were among the 150 victims of the crash. Airline Germanwings has said 35 of the 125 passengers identified were Spaniards. 

Earlier, Lufthansa CEO Carsten Spohr says the late take-off from Barcelona of the Germanwings plane that crashed in the French Alps was due to airport congestion and not related to the incident.  

Spohr added the crash of the plane that killed 150 people remained “incomprehensible.”

Spohr said Wednesday that “we still cannot understand” what happened in the “terrible accident.” He said it is “too early for speculation” about the cause.

The aircraft “had a clean maintenance bill” from an inspection the day before Tuesday’s crash and was “in perfect technical shape,” he said. No distress signal was received from the plane.

Spohr said he had a “very, very emotional meeting” with the relatives of the victims. 

Lufthansa, which owns Germanwings, has offered “immediate financial help” for those who need it.