"The co-pilot is alone at the controls," prosecutor Brice Robin said, drawing on information gathered from the black box recorder. "He voluntarily refused to open the door of the cockpit to the pilot and voluntarily began the descent of the plane."
Mr Robin said Lubitz had a "deliberate desire to destroy this plane. He ... refused to open the door of the cockpit to the pilot and deliberately began the descent of the plane".
Andreas Lubitz, the co-pilot of the doomed Germanwings airliner, competing in a Lufthansa marathon in 2013. Credit: Wolfgang Nass/BILD
The young Lubitz was brought up in the small town of Montabaur, 20 minutes' drive from the German city of Koblentz.
With his father a successful business executive and his mother a piano teacher his family could well afford the cost of flying lessons at his local club, Luftorts Club Westerwald.
Here he first started in the cockpit of a light aircraft at the age of 14 and after a couple of years of instruction under dual controls was able to fly on his own.
Klaus Radker, the club's chairman, said: "It was his dream to fly from an early age and it was a dream he began to fulfil here, so when he went on to gain his commercial licence and fly planes like the Airbus he was very happy and proud."
Andreas Lubitz competing in a Lufthansa marathon in 2013 (Wolfgang Nass/BILD)
Mr Radker last saw Lubitz in the autumn of last year, when the Germanwings pilot returned to the club to renew his light aircraft flying licence and take part in the club's barbecue, which he attended with a girlfriend.
Nobody at the club noticed anything strange in his demeanour.
"He seemed normal. Proud of his job after so much training. He seemed happy," said Mr Radker. "I always found him a friendly, if very reserve, person. Open and polite."
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Lubitz left Montabaur at the age of 20 in 2007 to begin his commercial pilot's training in the northern German city of Bremen.
It was a year into his training that he appears to have suffered the breakdown and took a break, before returning to qualify.
An investigator carries bags with items that have been collected in the house of the family of Andreas Lubitz (AP)
A mother of a schoolmate told the Frankfurter Allgemeine Zeitung that he had told her daughter he had taken a break from his pilot training because he was suffering from depression.
"Apparently he had a burnout, he was in depression," the woman, whom the paper did not name.
She said her daughter had seen him again just before Christmas and that he had appeared normal. She added he was a "lovely boy". "He had a good family background," she told the paper.
By the time of the accident he was still relatively inexperienced, having notched up only 630 hours of flying time, compared to the flight's captain, who had flown for more than 6,000 hours and had worked for Lufthansa for 10 years.
The captain was Patrick Sonderheimer, a father to two children, had joined Germanwings in May 2014. Previously he was a pilot with Lufthansa and Condor, a Lufthansa partner airline. He had been a pilot for 10 years.
Like many Mr Radker has also been left stunned by what happened above the French Alps on Tuesday, and he was anxious that a full and comprehensive investigation takes place before final judgment is passed on his fellow club member.
"Both the people who died and their friends and family survived deserved that, at the very least," he said. "I find it hard to believe that Andreas, who dreamt of flying and of being a pilot, would deliberately fly his plane into a mountain and kill all those people.
"If that is true it also means that the results of all the psychological tests he would have had to take to be a pilot were wrong."
The 27-year-old's parents' neighbours in the affluent suburb on the edge of Montabaur all spoke of a polite, if not particularly gregarious, man.
Johannes Rossbach, 23, who lives two doors away from Lubitz, said he would regularly see the pilot jogging through the neighbourhood's quiet streets.
Mr Rossbach said: "He was very polite. He would always say hello and goodbye. There certainly seemed nothing out of the ordinary about him."
He added: "I didn't realise he was a pilot until I heard it yesterday. And today's news is absolutely shocking. I can't believe someone like that would kill 149 other people. It's something that absolutely needs investigating and proving before we can believe it."
A police officer leaves a house believed to belong to Andreas Lubitz in Montabaur (Reuters)
It was Carsten Spohr, CEO of Germanwings parent company, in a press conference on Thursday who first said that Lubitz "took a break in his training six years ago. Then he did the tests (technical and psychological) again. And he was deemed 100 percent fit to fly".
"I am not able to state the reasons why he took the break for several months."
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Lubitz was identified as a German citizen and Mr Robin said he was not known to terrorism links or extremist links, but the prosecutor said he was expecting more information from the German authorities. Mr Robin added his religion was "unknown".
Lubitz also had a flat in Dusseldorf and he was an avid runner who often took part in local races, according to public records.
In 2007, Lubitz came 72nd out of 780 participants in a 10-kilometre New Year's week run in Montabaur, racing alongside his then 54-year-old father, Günter Lubitz, according to results posted by the organisers on its website that year.
He also ran the Lufthansa Frankfurt half-marathon in 2013, 2012 and 2011 alongside his father, finishing in times varying from just under 1 hour 49 to 1 hour 37 minutes, according to results published online.
On his Facebook profile, he said he was especially interested in the A320 and followed pilots chatroom in which they discussed technical aspects and different scenarios. His Facebook page has now been removed.
Late on Wednesday, it became clear that one of the pilots was locked out of the cockpit before the Germanwings plane descended and tried to get back in - to no avail, according to a senior source within the investigation team.
The pilot knocked on the door but there was no answer, according to the New York Times source after Flight 4U 9525 crashed on Tuesday near Digne-les-Bains in the French Alps. It was one of France's worst aviation disasters.
The source said: "The guy outside is knocking lightly on the door, and there is no answer. And then he hits the door stronger, and no answer. There is never an answer."
The information came to light after the cockpit voice recorder - 'black box' - was found after the Airbus A320 operated by the budget subsidiary of Lufthansa crashed during its route from Barcelona to Dusseldorf.
The voice data recorder of the Germanwings jetliner that crashed in the French Alps
According to Brice Robin, the French prosecutor, who revealed that the co-pilot crashed the place intentionally.
We heard the captain ask the co-pilot to take control, then we hear the noise of a seat that goes back and a door open, we can assume he went to relieve himself.
The co-pilot was alone. It is it this moment that the copilot manipulates the buttons of flight monitoring system to action the descent of the plane.
The action of this selectioner of altitude can only be deliberate. We hear the captain then speaks via an interphone to speak to the co-pilot, no response of copilot, he taps on door, no response of copilot, all we can hear is the sound of breathing, until impact suggesting the co-pilot was alive until impact."
Andreas Lubitz crashed the plane 'intentionally'Local authorities in Dusseldorf said the Germanwings co-pilot Andreas Lubitz was 27, and not 28 as reported earlier.
Lufthansa said both pilots were trained at the Lufthansa Flight Training School in Bremen.
The chief executive of Lufthansa has said there were no indications of abnormal behaviour in Lubitz and that there is "no system in the world" that could have predicted and prevented his actions.
"He was 100 percent fit to fly. There was no particular thing to note or to watch out for (in him)."
"We choose our staff very stricty. the choice of staff is very strict - we not only take into account their technical knowledge but also the pyschological aspect of our staff."
He said the psychological tests carried out on their pilots by a specialised German training centre were regarded as among the best in the world.
"The co-pilot qualified as a pilot in 2008. He first worked as a steward and then became a first officer (pilot) in 2013."
"He took a break in his training six years ago. Then he did the tests (technical and psychological) again. And he was deemed fit to fly."
"He took a several months break for reasons i do not know. Then he had to do the test again."
Mr Spohr said that in the US there is a rule that a steward remains in the cockpit when a pilot leaves, but that this is not the case in Europe and that he does not think it is necessary to change the procedures, despite the tragedy.
A model of a Germanwings plane is placed among flowers and lit candles in Cologne Bonn airport (REUTERS)
Peter Ruecker, a friend of Lutbitz from his home air club, LSC Westerwald, said he did not believe he was capable of such a thing" as flying was his "dream".
"He did his flight training in the club from an early age. He was a very calm and very precise young man. He took his baccalaureate here in Montabaur," Mr Ruecker told RTL radio.
"He was a perfectly normal young man. He was very happy with this job. He was satisfied and happy. He had achieved his dream: from an amateur pilot, he become a professional. He had no problems. I don't believe him capable of such a thing."
The German newspaper Bild reported the first officer was from Montabaur in Rheinland-Pfalz and cited the city mayor Gabriele Wieland speaking to the DPA press agency.
Carsten Spohr, CEO of Lufthansa, said the two pilots trained in Phoenix, Arizona and that the co-pilot started in 2008 after waiting for eight months. He first worked as a flight attendant.
"Since 2013 he was a first officer. After the training there was a long interruption (until he begun flying) but the person was fit to continue. He went through all medical checks and examinations. He was fit for flying without any interruptions," Mr Spohr added.
"His performance was without criticism - nothing at all was striking."
The Lubitzs' half a million euro detached home - a large, grey roof tiled building from where their son would set out for the short journey to the flying club, set on a plateau on one of the hills surrounding hills - is now a being treated as a potential crime scene.
On Thursday afternoon groups of plain clothes police officers began carrying out a forensic search of the house. They are also thought to be searching a flat Lubitz rented in Dusseldorf, 84 miles to the north.
"We are conducting a search of the parents' home," Ralf Herrenbrück, Dusseldorf chief prosecutor, told The Wall Street Journal. "All investigative measures are now under way."
Armin Pleiss, head teacher of the Mons-Tabor-Gymnasium high school where Lubitz graduated in 2007, said: "I am just as shocked and surprised as you are."
Laura, a neighbour whose brother was in the same year as Lubitz at the high school, added:
"I didn't know him well, but to me he seemed very private, perhaps a little bit withdrawn. But who would have guessed at something so shocking happening?"
The flying club which the first officer was a member of released a statement in tribute to him:
Andreas became a member of the association as a teenager, he wanted to realise his dream of flying. He began as a gliding student and made it to become a pilots on an Airbus 320.
He was able to fulfil his dream, the dream he has now so dearly paid for with his life. The members of the LSC Westerwald mourn Andreas and the other 149 victims of the disaster on March 24, 2015.
Our deepest sympathy goes out to the families. We will not forget Andrew. The members of the Luftsportclub Westerwald."
Additional reporting by Harriet Alexander, Rory Mulholland and Justin Huggler
