(CNN) — Latest developments:
• 7:55 a.m.: The co-pilot of the doomed Germanwings flight “accelerated the descent” of the plane when he was alone in the cockpit, Marseille prosecutor Brice Robin said Thursday. That can only be done deliberately, he said.
• 7:55 a.m: The co-pilot was alive until impact, Robin said, citing the sound of steady breathing in the cockpit.
• 7:55 a.m: There was a “deliberate attempt to destroy the aircraft,” Robin said.
Audio from the mangled voice recorder of Germanwings Flight 9525 reveals a bizarre struggle on board: One of the pilots was locked out of the cockpit and was trying to get inside when the plane crashed, according to media reports.
“You can hear he is trying to smash the door down,” a senior military official involved in the investigation told The New York Times.
“We don’t know yet the reason why one of the guys 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.”
Agence France-Presse also reported a pilot was locked out, citing a source close to the investigation.
Lufthansa, the parent company of Germanwings, said it was looking into the claim.
“We have no information from the bodies investigating the incident that would corroborate the report in the New York Times,” spokesman Boris Ogursky said. “We will not participate in speculation, but we will follow up on the matter.”
The Times’ report is a “terribly shocking revelation,” CNN aviation analyst Peter Goelz said. But he and other experts cautioned that it’s still unclear what could have been going on inside the cockpit.
An array of theories
Possibilities range from a medical emergency to something more nefarious, like a suicide mission, CNN aviation analysts said.
Officials previously said they hadn’t ruled out terrorism, but it seems unlikely.
French authorities have disclosed few details about what the recording actually contained.
“It is too early to draw conclusions to what happened,” said Remi Jouty, head of the BEA, the French aviation investigative arm leading the probe. “There is going to be detailed work performed on that audio file to understand and interpret the sounds and the voices that can be heard.”
Finding the plane’s second black box will also be critical to understanding the mystery of what went on inside the jet.
That box, the flight data recorder, hasn’t been found yet, but Lufthansa CEO Carsten Spohr said Wednesday that there’s a high probability it will be.
A dangerous search
Relatives and friends of the victims will embark on an emotional trip Thursday: flying over the scene where their loved ones perished.
Lufthansa will provide flights for them so they can be near the search scene, the company said.
While some human remains have been recovered, many have not. And the task is treacherous for search crews.
The plane crashed in the mountains of the French Alps, where slopes are steep and the weather has been icy.
The only way workers could get to the site was to drop down from helicopters. Jouty said they had to be together for safety.
Victims from 18 countries
The doomed flight was traveling from Barcelona, Spain, to Dusseldorf, Germany, when it crashed Tuesday in the French Alps.
Germanwings said the plane reached its cruising altitude of 38,000 feet, and then dropped for about eight minutes. The plane lost contact with French radar at a height of about 6,000 feet. Then it crashed.
There were 150 people from 18 countries on board.
Teams have begun the daunting task of identifying the victims’ bodies, but caution that it could take time to complete.
Clues in the debris
Investigators are still trying to piece together what caused the crash.
Jouty, the head of the investigation team, said the debris suggests the plane hit the ground and then broke apart, instead of exploding in flight.
Radar followed the plane “virtually to the point of impact” in the Alps in southern France, Jouty said. The flight’s last altitude recorded by radar was just over 6,000 feet.
FBI agents based in France, Germany and Spain are looking through intelligence sources and cross referencing the passenger manifest of Germanwings Flight 9525, two senior law enforcement officials said.
So far, one official said, the search hasn’t turned up anything that “stands out” or anything linking the passengers to criminal activity.