The co-pilot of the Germanwings plane that crashed in the French Alps on Tuesday, killing 150 people, appears to have deliberately flown it into a mountain after locking the flight commander out of the cockpit.
During the last eight minutes of the flight, the co-pilot "voluntarily" carried out actions that led to the destruction of the aircraft, Brice Robin, a French public prosecutor, said at a press conference in Marseille.
Citing evidence from a cockpit voice recorder recovered from the Airbus A320, Robin outlined the last moments of the doomed plane in a chilling account of the actions of the co-pilot, who he named as 28-year-old Andreas Lubitz.
Robin said Lubitz could be heard breathing right up until the point of impact, suggesting he had not lost consciousness. However, he failed to respond to increasingly desperate calls from the commander trying to break down the cockpit door, or to air traffic controllers.
Lubitz had been flying for Germanwings since September 2013 after being trained with the airline's parent company Lufthansa at its facility in Bremen. He had clocked up a total of 630 hours in the air.
Robin said Lubitz had "no reason to do it" and no links to terrorist groups. "There is nothing to suggest this was a terrorist act," he said.
"For the first 20 minutes of the flight, the pilots spoke in a normal way, you could say cheerful and courteous," Robin said. "We heard the flight commander prepare the briefing for landing at Düsseldorf and the response of the co-pilot seemed laconic. Then we heard the commander ask the co-pilot to take the controls.
"We heard at the same time the sound of a seat being pushed back and the sound of a door closing."
Robin said it was assumed that the flight commander needed to go to "satisfy natural needs" - in other words, use the toilet.
"At that moment, the co-pilot was alone at the controls and it was while he was alone that the co-pilot manipulated the flight monitoring system to action the descent of the plane. The action of selecting the altitude could only have been done voluntarily," Robin said.
"We heard several calls from the flight commander asking for access to the cockpit. There was a visual and audio interphone and he identified himself. There was no response from the co-pilot.
"The flight commander tapped on the door to demand for it to be opened but there was no response. We heard human breathing in the cabin and we heard this until the final impact, which suggests the co-pilot was alive."
Robin added: "The control tower at Marseille, receiving no response from the aircraft, asked for a distress code, and the activation of the transponder for a forced landing. There was no response. Air traffic control asked other aircraft in the area for a radio relay to try to contact the Airbus. No response came.
"Alarms went off signalling the aircraft's proximity to the ground, and we heard the sound of violent blows as if someone is trying to force the door. Just before the final impact we hear the sound of an impact on the [rock] embankment. There was no distress signal, no 'mayday, mayday mayday' received by air traffic control.
"Forty-eight hours after the crash ... the interpretation for us is that the co-pilot deliberately refused to open the door of the cockpit to the flight commander, and pushed the button causing a loss of altitude."
Lubitz did this, said Robin, "for a reason we do not know, but [it] can be seen as a willingness to destroy the aircraft".
"He had no reason to do this," said Robin. "He had no reason to turn the button making the plane go down, he had no reason not to allow his captain to return to the cockpit, he had no reason to refuse to reply to air traffic controllers, he had no reason to refuse to tap a code to alert other aircraft in the zone ... already that's a lot."
Robin added: "I don't think the passengers realised what was happening until the last moments because on the recording we can only hear cries in the final seconds."
Lufthansa said the co-pilot joined Germanwings in September 2013, directly after training, and had flown 630 hours.
The captain had more than 6,000 hours of flying time and been a Germanwings pilot since May 2014, having previously flown for Lufthansa and Condor, Lufthansa said.