Evidence from the recently recovered black box in the crashed Airbus showed that the co-pilot “deliberately” destroyed the plane as passengers screamed in terror behind him.
At a press conference, Brice Robin, the procureur examining judge said that the co-pilot Andreas Lubitz, 28, intentionally put the plane into a descent while the pilot was out of the cockpit.
He added that Lubitz had refused to let the captain back in the cockpit despite him hammering on the armoured door and trying to break through.
Mr Robin said the co-pilot was alive but did not speak a word until the Germanwings jet hit the ground in the south of France.
“While he is alone, the co-pilot presses the flight monitoring system buttons to put into action the descent of the aeroplane. This action on the altitude controls can only be deliberate.”
Mr Robin said there was “absolute silence in the cockpit” but the recordings suggested there were screams from the passenger cabin.
Lubitz joined Germanwings straight from training in September 2013 and had flown for more than 600 hours.
US newspaper New York Times and news agency AFP both both reported today that the captain could not get back in through the locked door during the eight-minute plunge that killed 150 people.
The New York Times report said that the start of the flight on Tuesday went as normal with the crew speaking normally in German. One of the seats is heard being moved and the cabin door is heard opening.
But when the second pilot tried to return and tapped lightly on the door there was no response – and none when he hit the door harder and tried to smash through the armoured anti-hijack door.
The source said there were no sounds from inside the cockpit until proximity alarms sounded as the plane neared the ground. It crashed into the Alpine foothills near Seyne-Les-Alpes in Alpes-de-Haute-Provence.
President Hollande, German Chancellor Angela Merkel and Spanish Prime Minister Mariano Rajoy visited Seyne-Les-Alpes and flew over the crash site yesterday.
Of the passengers killed 72 were German citizens, including 16 pupils heading home from an exchange trip, with 51 Spanish. Three victims were British with others from Australia, Argentina, Colombia, Denmark, Holland, Iran, Israel, Japan, Mexico, US and Venezuela.
Families of the victims have been arriving at Seyne-Les-Alpes and nearby Le Vernet, the two towns closest to the crash site, where residents have been offering spare rooms and holiday cottages to house them for free. Some who speak German or Spanish have offered to act as interpreters.
The four hectare crash site at 1,500m above Seyne-Les-Alpes is being searched by 600 gendarmes and police, 100 pompiers and Chasseurs Alpins soldier who are looking for remains and the second black box.