French prosecutor Brice Robin said the passengers on flight 4U 9525 only realised "at the last moment" they were about to crash, because "we only hear the screams on the last moments of the recording".

Image source, AFP

Richard Westcott
BBC Transport Correspondent

This kind of event is rare but it has happened before, although the reasons vary widely. After 9/11 they made cockpits impregnable. It keeps the terrorists out, but in the end it also allows someone to keep their colleagues out too. Airlines have to make a call. Which is the bigger threat - terrorism or suicide?

Richard Westcott
BBC Transport Correspondent

The focus now moves from the mechanics to the man flying the plane. An accident expert has told me the investigators will pore over the co-pilot's background and that of his family too. Did he owe money? Was there a grudge? They'll look at his religion, whether he was in trouble with the law, whether he had a stable love life.

Sean Maffett, an aviation analyst, says a change in staffing levels might help prevent such incidents in future. "One possible answer to this is to insist all flights have three pilots on board, so there are always two of them on the flight deck. But airlines are run by accountants - that's horrendously much more expensive. It's a problem that is not going to be resolved straight away."

German police have been deployed outside what is thought to be Andreas Lubitz's home in Montabaur, in west Germany.

Image source, AP

German Interior Minister Thomas de Maiziere says there are no indications that the co-pilot, Andreas Lubitz, had "any kind of terrorist background", the Reuters news agency reports.

Aviation analyst Sean Maffett says there is no requirement for psychiatric tests on pilots. "There have been calls for them in the past, and the calls will be renewed for that to happen," he tells the BBC. "I know that in the pilot fraternity there is considerable worry that that is going to happen, because it'll do nothing for most people but make their lives much more difficult."

According to the audio recording from the flight recorder, the captain is heard asking the co-pilot to take over controls of the plane. Then there is the sound of a chair being pushed back and a door being closed. Moments later the captain is heard knocking on the door and asking to be let in, but receives no answer from the co-pilot.

Germanwings flight 4U 9525 crashed on Tuesday into the French Alps en route from Barcelona to Duesseldorf. The German authorities are now taking charge of the investigation into co-pilot Andreas Lubitz, according to French prosecutors.

Image source, AFP

Mr Robin said pounding on the cockpit door could be heard during the final minutes of the flight of the Germanwings airliner, and that alarms sounded. He also said the co-pilot's breathing was normal throughout the final minutes.

During the news conference, Mr Robin refused to give details on Andreas Lubitz's religion, saying: "I don't think it's necessarily what we should be looking for."

Information taken from the black box cockpit voice recorder indicated that the co-pilot Andreas Lubitz did not say a word once the captain left the cockpit, Mr Robin said. "It was absolute silence in the cockpit."

According to Lufthansa, which owns Germanwings, the co-pilot joined the airline in September 2013, immediately after training, and had flown 630 hours.

Image source, AFP

Brice Robin said the responses of the co-pilot, named as Andreas Lubitz, 28, were initially courteous but became "curt" when the captain began to give a mid-flight briefing, about the planned landing of the Germanwings flight. The plane's eventual crash in the French alps killed 150 people.

Mr Robin also said the co-pilot "pushed the button to trigger the aircraft to lose altitude. He operated this button for a reason we don't know yet, but it appears that the reason was to destroy this plane".

Brice Robin, the state prosecutor in Marseille, told a news conference the co-pilot was alone at the controls when the plane came down. Analysis of the flight recorder showed the pilot had left the cockpit and was then calling on the co-pilot to let him back in, but there was no reply, he added. The co-pilot was heard breathing - showing that he was still alive at the time of the impact. "The most plausible interpretation is that the co-pilot through a voluntary act had refused to open the cabin door to let the captain in," Mr Robin said.

Image source, AP

Welcome to the BBC's live coverage of reaction to the announcement by prosecutors in the French city of Marseille that all the evidence from the cockpit voice recorder from the crashed Germanwings airliner suggests the co-pilot was responsible for the disaster, purposely steering the plane into the Alps.