The first mystery was material and lasted only 48 hours. How could an Airbus A320 with a flawless maintenance record drop 10,000m in eight minutes without veering from its flight path, without emitting a Mayday signal and without responding to air-traffic controllers, then smash into a rocky mountainside, killing all 150 people on board?

The second mystery was human and will never be fully solved. The medical records and personal documents of Andreas Lubitz, the plane’s co-pilot, that police have seized may go some way to explaining his state of mind, but the German public and families of the victims may never understand how an apparently normal 27-year-old could betray the trust invested in him, deliberately extinguishing the lives of 149 innocent people.

Was the suicide crash premeditated or a spur-of-the-moment impulse? Did Lubitz want to die in the alps of Haute Provence because of their wild beauty and inaccessibility? Or was the steep and isolated valley an arbitrary, last-minute choice?

The technical investigation continues, but the focus is now clearly on Lubitz's mind. His employers at Lufthansa have said that German privacy laws prevented them revealing his medical records. Numerous press reports speak of psychological fragility. German state prosecutors said on Friday that they had found evidence that Lutbitz hid a medical condition from his employers.

The tabloid Bild has reported that Lubitz spent 18 months in psychiatric treatment and was held back several times during training for depression. Bild also claims that Lubitz was going through a "personal life crisis" in his relationship with a girlfriend who had often been seen jogging with him.

Perhaps the German police will find a rambling letter in the slate-roofed white bungalow, with its manicured garden where, Lubitz lived most of the time with his parents and younger brother, in the Rhineland town of Montabaur. Police also removed items from the top floor pied-a-terre in a handsome building in Düsseldorf that Lubitz bought with his co-pilot’s salary.

Crash site

At the crash site, high in the alps of Haute Provence, French authorities have made a priority of finding Lubitz’s remains. Chemical analysis would show if he took psychotropic drugs that alter brain functions.

Lubitz’s background is as German as strudel and lederhosen. His father is a bank employee, his mother an organist for the local Lutheran church. As a youth Lubitz delivered newspapers for the same church.

Flying was the passion of Lubitz’s life. He joined Luft Sporting Club Westerwald, a local glider association, at the age of 14.

Before they learned the horrible truth about the crash, LSC Westerwald posted a death notice on its website. “Andreas became a member of the club as a youth to fulfil his dream of flying,” it said. He had “fulfilled his dream, the dream he now paid for so dearly with his life”.

Lubitz's parents and brother also mistook him for an ordinary victim of an accidental plane crash. They travelled to France, where they were separated from the families of Lubitz's victims.

The other families were briefed by Brice Robin, the prosecutor, on arrival at Marseilles Provence Airport, before Robin made his terrible findings public in a press conference on Thursday.

Tuesday's crash, with the loss of 150 lives, had already plunged Europe – especially Germany and Spain – into shock. Seventy-five of those who died on the Barcelona-to-Düsseldorf flight were German; 50 were Spanish, according to Spanish authorities.

For two days aviation experts and media speculated on a possible depressurisation of the plane, computer failure or a terrorist attack. But the scenario Robin outlined raised shock to a new level.

According to the Marseilles prosecutor entrusted with the judiciary investigation, the cockpit voice recorder showed that Lubitz talked cheerfully with the pilot for 20 minutes. The last radio contact with air-traffic control occurred at 10.30am.

Then one hears the pilot’s seat slide back and the door opening and closing as he went to the toilet. At 10.31am the A320 began its descent. According to Robin, Lubitz had deliberately activated the descent button. The descent continued for eight minutes, after which the aircraft levelled out at 1,800m.

In the meantime the pilot had returned from the toilet. Lubitz would have seen him via video camera, requesting to re-enter the cockpit. The co-pilot remained silent. The pilot tapped on the door. Still no response. Lubitz ignored calls from the Marseilles control tower. The pilot pounded on the door, then tried to break it down.

In the last seconds, as snow-covered mountains towered above them, passengers began screaming. Lubitz’s steady breathing, audible on the recording, excluded the possibility that he suffered a heart attack or lost consciousness, Robin said.

In the wake of the 9/11 attacks the US had persuaded airlines around the world to install armoured doors with automatic locks. It is perhaps the greatest irony of the Germanwings crash that a security measure designed to foil hijackings facilitated the murder of 149 people.

Pilots’ unions – but neither Lufthansa/Germanwings nor any of the governments involved – questioned Robin’s interpretation of the voice recorder and cautioned against rushing to judgment. They offered no alternative explanation.

Kamikaze mission

Lubitz appears destined to go down in history as the mass murderer who, 14 years after 9/11, took a civilian airliner on a kamikaze mission, albeit not for political or ideological reasons. He more resembles gunmen who have mown down civilians in US shopping centres, cinemas and university campuses. Or Anders Breivik, the deranged Norwegian who killed 77 people in 2011.

Robin’s revelations transformed Germany’s profound sadness at what it had believed to be an absurd accident into incredulousness and fury. “When will this nightmare end?” asked Bodo Klimpel, the mayor of Haltern-am-See, the home of 16 secondary-school students who died in the crash. “It makes me furious that a suicidal person could take 149 people with him,” said Ulrich Wessel, the principal of Joseph-König-Gymnasium.

There were cultural differences in the way Germany, Spain and others among the 15 countries of origin addressed the tragedy. In Germany 20 policemen guarded the school, to protect schoolmates from traumatic encounters with the press. Photographs of the 14 girls and two boys, all aged 15 and 16, were pixellated and their identities kept secret.

Lufthansa/Germanwings was also squeamish about revealing information. Even in death, employees’ medical records remain secret, said Carsten Spohr, Lufthansa’s chief executive.

Another airline official refused, on the grounds of privacy laws, to confirm that the widely published photograph of a smiling Lubitz in front of the Golden Gate Bridge was the co-pilot.

Although half of the fatalities were German, very few of their identities were revealed. They included two opera singers, Oleg Bryjak, a baritone, and Maria Radner, the contralto, whose husband and baby died with her.

The Spanish were more public in their mourning, releasing photographs of, among others, Marina Bandrés López-Belio, who had returned to Spain with her nine-month-old baby and took the Germanwings flight because it was the most rapid route to return to her husband in Manchester.

The Moroccan consul in Barcelona announced that two Moroccan citizens, 24-year-old Mohamed Ettahrioui and his bride, 23-year-old Asmaa Ouahoud El Allaoui, had held a family wedding in Barcelona three days before they boarded the flight to Düsseldorf, where they planned to start married life.

Crash site

The inhabitants of the Alpine villages near the crash site are accustomed to seeing small dots followed by white vapour trails overhead. But last Tuesday a farmer, a lumberjack and others were startled to see the unusually large and low aircraft moving south to north. It was too low; it wouldn’t clear the Mariaud pass, several remembered thinking.

But like the ploughman who sees Icarus falling in WH Auden’s poem, they returned to their occupations. No one heard the plane crash.

François Balique, the mayor of Le Vernet, the tiny hamlet closest to the crash site, calls his homeland “a little piece of Switzerland that got lost in Haute Provence”. Set against a backdrop of razor-sharp snow-covered peaks, the villages of the Seyne-les-Alpes canton make a living from sheep and cattle farming, tourism and the mineral-water plant at Montclar.

The Germanwings crash unsettled their quiet lives. “There’ve never been so many people here before,” said Michelle Chauvin, a nurse. She and her husband, Philippe, a retired forester, both in their late 50s, have never taken a plane journey, “and we’re not going to start now”.

Close to 1,000 gendarmes, firemen and French military flooded to the area to join the search and recovery operation, which is conducted almost exclusively by helicopter. The gendarmes wear blue, the firemen fluorescent orange, the military green. They were outnumbered by journalists.

On Thursday about 300 family members travelling from Spain and Germany made the pilgrimage to Le Vernet, where, a day after the heads of state and government of France, Germany and Spain, they stood for a long time in the pasture facing the mountain behind which their loved ones perished. Local residents rose to the occasion, volunteering to cook for rescue workers and offering rooms for the family members.

The technical inquiry and the search for the flight-data recorder continue. Gendarmes and firemen have cordoned the crash site into grids, each of which will be combed for fragments of bodies and the aircraft.

The most often-heard phrase is that the plane was “pulverised”, like the lives of the victims. In discussing their task, rescue workers use banal comparisons to describe the dismembered humans and aircraft. No part of the plane is bigger than a car door, said Xavier Roy, the co-ordinator of helicopter operations. No part of a human is bigger than a suitcase, said a gendarme returning from the crash site.

Refrigerated lorries ply the winding mountain roads, ferrying body parts to a forensic lab in Marseilles for identification. The victims’ families were asked to bring photographs and dental records, and to provide DNA samples. Unusual jewellery and prosthesis can also be used to identify the dead.

Alpine catastrophe

Following shortly after the

Charlie Hebdo

and Bardo National Museum massacres, in Paris and Tunis, the Alpine catastrophe brought another stele – or memorial pillar – more candles, minutes of silence, flags at half mast and national days of mourning. So this is life in the 21st century. “We have known a certain number of trials recently,” President François Hollande said when he visited the site.

Frédéric Petitjean, a fire-department rescue doctor, participated in France’s Ebola effort in west Africa. “You get used to death,” he said. A 10-year-old schoolboy in Le Vernet uttered exactly the same sentence.

Msgr Jean-Philippe Nault, bishop of nearby Digne-les-Bains, visited Le Vernet “to show our presence, our proximity, to the families and to the people from here who are also affected”.

As a man of faith, I asked him, how could he explain 150 lives snuffed out in an instant? “One mustn’t seek explanation,” the bishop answered. “There are no appropriate words.”