Cockpit voice recordings from the German jet that crashed in the Alps showed one of the pilots left the cockpit and could not get back in before the plane went down, killing everyone onboard, the New York Times reported, reports Reuters.
The recordings did not make clear why the pilot left the cockpit or why he could not regain entry as the plane steadily descended toward a mountain range in a remote area of the French Alps on Tuesday.
Investigators were studying the voice recordings from one of the "black boxes" for answers on Thursday while the search continued for a second black box.
"The guy outside is knocking lightly on the door and there is no answer," an unnamed investigator told the Times, citing the recordings. "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.
A spokesman for Lufthansa, whose budget arm Germanwings operated the flight, said the carrier was aware of the Times story, adding: "We have no information from the authorities that confirms this report and we are seeking more information. We will not take part in speculation on the causes of the crash."
Asked to comment on the investigation, French Finance Minister Michel Sapin told iTELE on Thursday: "The best thing for now is not to rule out any hypothesis."
The retrieval of one of two cockpit recordings came as French President François Hollande, Germany's Angela Merkel and Spain's Mariano Rajoy travelled on Wednesday to the crash site to pay tribute to the 150 victims, mostly Germany and Spanish.
France's BEA air incident investigation bureau was not immediately available for comment on the Times report but earlier had said it was too early to draw meaningful conclusions on why the plane went down.
"We have just been able to extract a useable audio data file," BEA director Rémi Jouty told a news conference at the agency's headquarters outside Paris on Wednesday.
"We have not yet been able to study and to establish an exact timing for all the sounds and words heard on this file."