The co-pilot of the Germanwings
flight that crashed in the French Alps, named as Andreas Lubitz,
appeared to want to "destroy the plane", officials said.
Marseille
prosecutor Brice Robin, citing information from the "black box" voice
recorder, said the co-pilot was alone in the cockpit.He intentionally started a descent while the pilot was locked out.
Mr Robin said there was "absolute silence in the cockpit" as the pilot fought to re-enter it.
He said air traffic controllers made repeated attempts to contact the aircraft, but to no avail. Passengers could be heard screaming just before the crash, he added.
Details are emerging of the German co-pilot's past - although his apparent motives for causing the crash remain a mystery.
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Mr Lubitz, 28, had undergone intensive training and "was 100% fit to fly without any caveats", according to Carsten Spohr, the head of Lufthansa, the German carrier that owns Germanwings.
Mr Spohr said Mr Lubitz's training had been interrupted for several months six years ago, but was resumed after "the suitability of the candidate was re-established".
German Chancellor Angela Merkel told reporters that the co-pilot's apparent actions had given the tragedy a "new, simply incomprehensible dimension".
Police have been searching the co-pilot's home for evidence, German prosecutors told the Reuters news agency.
The Airbus 320 from Barcelona to Duesseldorf hit a mountain, killing all 144 passengers and six crew, after an eight-minute descent.
Andreas Lubitz: Germanwings co-pilot under scrutiny
- Started training in 2008, at Bremen and Arizona. Training briefly interrupted - but deemed fit to fly
- Working as co-pilot, or first officer, since 2013. Appeared pleased with his job
- Lived in town of Montabaur, near Frankfurt, reportedly with his parents. Kept a flat in Duesseldorf and had many friends
- Facebook profile suggests the active lifestyle of a keen runner, with an interest in pop music
"We hear the pilot ask the co-pilot to take control of the plane and we hear at the same time the sound of a seat moving backwards and the sound of a door closing," Mr Robin told reporters.
He said the pilot, named in the German media as Patrick S, had probably gone to the toilet.
"At that moment, the co-pilot is controlling the plane by himself. While he is alone, the co-pilot presses the buttons of the flight monitoring system to put into action the descent of the aeroplane.
Crash site close-ups
"One person can't have the right to end the lives of hundreds of people and families," Esteban Rodriguez, a Spanish factory worker who lost two friends aboard the aircraft, told the Associated Press news agency.
The principal of a German high school that lost 16 students and two teachers in the crash said the latest news was "much, much worse than we had thought".
Residents of Alpine villages near the scene of the crash have also expressed shock.
"For the pilot it's suicide, perhaps, but it's an attack on the other people. Yes, an attack," Charles Bosshardt, a mountain risk adviser, said. "It's horrible, there are no words."
Lufthansa has arranged two special flights for families and friends on Thursday - one from Barcelona and one from Duesseldorf - to Marseille, and both groups will travel on by road. Separately, some relatives who did not want to fly are travelling by bus from Barcelona.
The second "black box" - that records flight data - has still not been found.