The co-pilot of Germanwings Flight 9525 deliberately sent the jet crashing into the mountains to destroy the plane, French prosecutors believe.
Andreas Lubitz, 27, put the plane into a descent after locking the captain out of the cockpit, Marseille prosecutor Brice Robin told reporters.
Evidence from the black box flight recorder suggests he then refused to open the cockpit door to the captain, who can he heard pounding on the door in a desperate attempt to break in.
Mr Robin said: “The most probable interpretation is that the co-pilot refused to open the cockpit door to the pilot and actioned the button which started the descent procedure.
“We can only deduct that it destroyed this plane.”
The recording also suggests the passengers were unaware of what was happening until the final moments, when their screams can be heard.
The plane crashed on Tuesday en route from Barcelona to Dusseldorf, killing all 150 people on board.
Mr Robin said the cockpit voice recorder gave information from the first 30 minutes of the flight.
For the first 20 minutes the two pilots talked in a normal fashion and were as courteous as two pilots would be.
He said the co-pilot’s responses, initially courteous, became “curt” when the captain began the mid-flight briefing on the planned landing.
The captain is then heard asking the co-pilot to take over and the sound of a chair being pushed back and a door being closed is heard.
It was assumed that the captain had gone to the toilet, leaving the co-pilot in charge of the plane, the prosecutor said.
Mr Robin went on: “The co-pilot uses the flight monitoring system to start the descent of the plane. This can only be done voluntarily, not automatically.
“We hear several cries from the captain asking to get in. Through the intercom system he identifies himself – but there is no answer. He knocks on the door and asks for it to be opened – but there is no answer.”
Mr Robin said that after entry to the cockpit was denied, the sound of breathing from inside the cockpit was heard and this sound carried on until the moment of impact.
“The co-pilot was still alive at this point,” Mr Robin said.
He said there was no distress signal, no Mayday and no answer despite numerous calls to the plane from ground controllers.
The cockpit voice recorder also shows that there were alarm signals going off indicating the proximity of the ground.
Noises of someone trying to break down the cockpit door are heard then finally the sound of an impact. Mr Robin said the plane may have glided before the moment of impact.
Asked about Mr Lubitz’s ethnicity, Mr Robin said: “He was a German national and I don’t know his ethnic background.
“He is not listed as a terrorist, if that is what you are insinuating.”
Pressed again on the co-pilot’s religion, he said: “I don’t think this is where this lies. I don’t think we will get any answers there.”
He said German authorities were taking charge of the investigation of Lubitz.
Mr Robin said black box recordings showed that Lubitz “was breathing normally, it wasn’t the breathing of someone who was struggling”.
Speaking about whether the passengers realised what was happening, Mr Robin said: “I think the victims only realised at the last moment because on the recording we only hear the screams on the last moments of the recording.”
He added: “I believe that we owe the families the transparency of what the investigation is pointing to and what is going on, we owe it to them to tell them what happened.
“The families have been informed of everything I just told you.”