On board for the short-haul flight from Barcelona to Dusseldorf were 144 passengers and six crew. Among them were three Britons, including seven-month-old baby Julian Pracz-Bandres, and 16 children and two teachers from the Joseph König Gymnasium in Haltern am See, who were returning to Germany after a week-long foreign exchange in Spain. Haltern am See’s mayor would later describe Tuesday’s events as “the darkest day in the history of our city”.

Andreas Lubitz’s remains are scattered across the mountains, along with those of his victims. What turned him from an apparently successful pilot, with a promising career ahead of him, into a mass murderer at the age of just 27 is the subject of inquiries by authorities across a number of jurisdictions.

^{Manchester mother Marina Bandres died with her baby son in the Germanwings plane crash}

From a variety of sources – official and unofficial – we now know that Lubitz suffered from depression, had had some kind of “burn-out”, and was being treated for an unspecified illness that should have prevented him from flying on that fateful day.

He was a man apparently in torment. One former girlfriend claimed that Lubitz had become increasingly volatile and had talked grandiosely of doing “something that will change the whole system and then all will know my name and remember it”.

The starting point for investigators trying to understand Lubitz’s mindset will be his home town, Montabaur, in the Rhine, half-way between Cologne and Frankfurt. His father Günter, 54, and mother Ursula were due to be interviewed by the police on Saturday afternoon. Mr and Mrs Lubitz had travelled to France with other grieving relatives, only to arrive there and discover that their son had been identified as the killer.

He lived with his parents in an affluent suburb of the town, in a house worth half a million euros. His father is a wealthy businessman; his mother a piano teacher who plays the organ in the local church. The couple had two sons, of whom Andreas was the older. “He was a good boy from a good family,” said the mother of a former classmate at Mons Tabor Gymnasium, the local grammar school.

He was, from a very young age, obsessed with flying. “He was a real fanatic,” said a friend. “His room was plastered with pictures of planes and the Lufthansa logo everywhere. Pictures of old planes, new planes, of the largest planes – everywhere you could see aviation stuff, even over his bed.”

^{Paul Andrew Bramley, aged 28, was a passenger on Flight 4U9525}

At the age of 14, Lubitz joined the local flying club, Luftorts Club Westerwald, a short drive from the family home. After a year of lessons under dual controls, he was able to fly a glider on his own. “It was his dream to fly from an early age. So when he went on to gain his commercial licence and fly planes like the Airbus he was very happy and proud,” said Klaus Radker, the flying club’s chairman.

^{A glider that was flown by Andreas Lubitz in the hangar of the club in Montabaur (AP)}

Lubitz applied for a job at Lufthansa, the German national airline that also owns the budget airline Germanwings. Lufthansa is reckoned among pilots to be just about the best carrier to work for. Lubitz passed a number of rigorous assessments – including psychometric testing of a candidate’s ability to work under pressure and handle stress – to be accepted on its pilot training programme. Only between 4 and 8 per cent of those who apply are offered a place, and Lubitz was one of them.

In 2008, he enrolled with Lufthansa’s prestigious flight training school in Bremen and, as part of that training, moved in July 2010 to its Airline Training Center Arizona, not far from Phoenix.

^{Lubitz’s Facebook profile picture was him sitting beside San Francisco’s Golden Gate Bridge}

But despite his success in getting into flight school, there were serious signs emerging that Lubitz was a deeply troubled young man. In 2009, part-way through his training, he suffered a “serious depressive episode” and began to receive some form of counselling or psychiatric treatment, according to the German tabloid newspaper Bild.

Another source said: “During his training at Lufthansa flight school, Andreas was listed as unsuitable for flight duties, because he spent one and a half years in psychological treatment, and so he had to repeat courses.”

Der Spiegel reported that he had suffered “burn‑out syndrome”. A special coding, “SIC”, was entered on his licence, meaning that he needed a “specific regular medical examination”, according to Germany’s federal aviation office.

^{The “Black box” from Flight 4U9525}

The airline has been more circumspect. Carsten Spohr, Lufthansa’s chief executive, said: “Six years ago there was a lengthy interruption in his training. After he was cleared again he resumed training. He passed all the subsequent tests and checks with flying colours.”

He added: “He took several months’ break for reasons I do not know. Then he had to do the tests again.” In comments that will come back to haunt him, Mr Spohr had insisted Lubitz was “100 per cent fit to fly without any limitations”. That claim has turned out to be false.

On qualifying, Lubitz did not land a job as a pilot immediately and worked as a cabin steward until a vacancy arose. It earned him the nickname “Tomato Andi”, possibly because one of his roles was to hand out tomato juice. It has also been suggested “Tomato” is a derogatory term, meaning someone who isn’t sure if he was a “fruit” or not. There is no evidence, so far at least, that Lubitz was gay and kept his homosexuality hidden, but it’s inevitably an area for the police to explore.

Whatever the truth, for Lubitz, a young man wanting to fly transatlantic jets, to find himself working as a “trolley dolly” would have been all too demeaning.

In September 2013, a vacancy finally appeared for a pilot, albeit with Lufthansa’s less glamorous sister airline, Germanwings, which flies short-haul budget flights across Europe.

For Lubitz, recovering from depression and a long stint as an air steward, the realisation that he had not landed the dream job he had hankered after ever since childhood might have hit him hard.

If it did, Lubitz was keeping his feelings to himself. At a barbecue at the gliding club in Montabaur last summer, Lubitz appeared to have it all. “He seemed normal; proud of his job after so much training. He seemed happy,” recalled Klaus Radker. He was accompanied by a girlfriend, thought to be a teacher, and though quiet and reserved (his normal demeanour), everybody remarked on how happy he seemed.

^{A police officer stands next to the block of flats where Lubitz lived in Dusseldorf (AP)}

By then, Lubitz had moved into a flat in Dusseldorf, where Germanwings has a hub airport. It is thought the partner whom he took to the barbecue lived with him. Nobody at the apartments last week would talk about their neighbour. Police had sealed off the flat and there was no evidence of a girlfriend living there, although the nameplate “Goldbach” sits with his at the entrance. Bild newspaper claimed that, at the time of the crash, Lubitz had broken up with her. He was said to be suffering, said the newspaper, from a “personal life crisis”.

A previous girlfriend, known only as Maria, gave an astonishing account of Lubitz as a man fighting his demons as their five-month relationship soured. She was an airline hostess, living near Frankfurt, and they had met on a flight, sparking a tempestuous romance that comprised fleeting assignations in hotel rooms around Europe and Germany.

^{Germanwings employees cry as they place flowers and lit candles outside the company headquarters in Cologne}

Maria said she thought he had crashed because he knew his illness would prevent him progressing to Lufthansa jets. “He did it because he realised that because of his health problems his big dream of a job with Lufthansa, a job as captain and as a long-haul pilot, was as good as impossible,” she said.

Lubitz was a man, who appeared “nice and open-minded” in public, but needed constant reassurance in private. “He was a good man who could be very sweet,” she said. “We spoke a lot about work, and then he became another person. He became agitated about the circumstances in which he had to work, too little money, anxiety about his contract and too much pressure.”

They split up when she felt unable to deal with his growing problems and his increasingly volatile temper any more. “During conversations he’d suddenly throw a tantrum and scream at me. I was afraid. He even once locked me in the bathroom for a long time.” At night he would wake up in a sweat, screaming in terror “We’re going down”, she said, and he also threatened a spectacular gesture to “make everyone remember” him.

Just weeks before Tuesday’s crash, Lubitz had bought two Audis from a local dealership, one for him and one for his now ex-partner, the teacher, in a desperate bid to win her back. Only one of the cars was delivered, suggesting that she had declined his gift.

Police are investigating claims that he went on a spending spree in the weeks before the crash. Fabrizio Poli, an aviation expert with his own private jet company, said Lubitz would have been earning in the region of €130,000 (£95,000) as a Germanwings pilot, despite his junior ranking. But a large slice of that would have gone to Lufthansa to repay his training.

By the time of the crash, Lubitz, a fitness fanatic, was clearly struggling with an as yet unidentified illness, and one that he kept secret from his employers. If he couldn’t fly, his worries about money would inevitably have been compounded. Certainly, on the day of the crash, Lubitz had been given a sick note excusing him from going to work. Instead of handing it in, he ripped it up. Five other medical notes were also found torn up.

“Documents with medical contents were confiscated that point towards an existing illness and corresponding treatment by doctors,” said the prosecutors’ office in Dusseldorf. “The fact that there are sick notes saying he was unable to work that were found torn up, which were recent and even from the day of the crime, supports the assumption based on the preliminary examination that the deceased hid his illness from his employer and his professional colleagues.”

What that illness was is unclear. Dusseldorf University Hospital, where he had been treated in February and most recently on March 10, said in a statement that Lubitz had gone to the hospital for “diagnostic evaluation”.

It declined to provide details about his condition, but denied German media reports that it had treated the pilot for depression.

Die Welt, quoting German police sources, reported on Saturday that investigators had found evidence that Lubitz had a “serious psychosomatic illness” and that medication for the treatment of “severe burn‑out syndrome” had been discovered in Lubitz’s flat. Some experts have claimed burn-out can cause suicidal tendencies, but others say the condition is not medically recognised.

But The New York Times offered an alternative explanation for his treatments in February and March, suggesting that Lubitz was suffering from “vision problems”. Deteriorating eyesight would have cut short his career and, for a man who had only ever wanted to be a pilot, such a condition would have been devastating.

His medical files have been passed to the authorities examining the crash. They will try to work out what was going on when he took control of Flight 4U9525 and flew it into a mountain.

• Plane crash film released days after Germanwings disaster

Lubitz had to wait for the plane’s captain to leave the cockpit for a break, an event that had happened routinely on previous flights. But it would indicate that the decision may not have been pre-planned, because had Capt Sonderheimer not needed to answer a call of nature then Lubitz would not have been left alone to crash the plane into an area of the French Alps he knew well from days on gliding holidays there.

Phillip Hodson, a psychotherapist and fellow of the British Association of Counsellors and Psychotherapists, said: “I think it’s quite possible he didn’t plan this. The nature of depression can lead to people taking action on impulse.

“He is a person pretty buttoned up and closed, who hid his symptoms. He is disciplined and hard-working but he has a very brittle ego. He believes he is a brilliant pilot, but he first has to spend time serving passengers as a ‘trolley dolly’, and that must rankle, and then he gets a pilot’s job but only with a budget airline, not Lufthansa itself.”

As he sat in the pilot’s seat, in sole charge of a multimillion-pound aircraft, responsible for the lives of 149 other people, Lubitz had made a decision to damn them all. He wanted to die and here was his opportunity. The question for the authorities trying to understand his actions is, was he so caught up in his own world, and his own misery, that he didn’t care what happened to the lives of others – or did he deliberately make a statement declaring his own importance by killing them too?

The silence on the black box recorder, and the seeming absence of a suicide note, leaves those questions unanswered.

But in those eight minutes of silence, Lubitz revealed himself to the world as a calm, cold-blooded killer, who will go down in history – perhaps just as he wanted – as a “madman” who destroyed the lives of 149 innocent individuals.

Additional reporting by Patrick Sawer, Greg Walton, Justin Huggler and Rory Mulholland