The Germanwings co-pilot who flew his Airbus into the French Alps, killing all 150 aboard, hid a serious illness from the airline, prosecutors have said, amid reports he was severely depressed.

The black box voice recorder indicates Andreas Lubitz, 27, locked his captain out of the cockpit on Tuesday and deliberately sent Flight 4U 9525 crashing into a mountainside, French officials say, in what appears to have been a case of suicide and mass murder.

French Prime Minister Manuel Valls said that “everything is pointing towards an act that we can’t describe: criminal, crazy, suicidal.”

German prosecutors revealed on Friday that searches of Lubitz’s homes netted “medical documents that suggest an existing illness and appropriate medical treatment”, including “torn-up and current sick leave notes, among them one covering the day of the crash”.

Bild daily reported that Lubitz sought psychiatric help for “a bout of serious depression” in 2009 and was being helped by doctors, quoting documents from Germany’s air transport regulator.

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The paper also cited security sources saying Lubitz and his girlfriend were having a “serious crisis in their relationship” that left him distraught.

Lufthansa CEO Carsten Spohr said Lubitz had suspended his pilot training, which began in 2008, “for a certain period”, before restarting and qualifying for the Airbus A320 in 2013.

According to Bild, those setbacks were linked to “depression and anxiety attacks”.

On Thursday Spohr said Lubitz had all the psychological tests required for training and was 100-per-cent airworthy.

Lubitz lived with his parents in his small home town of Montabaur and kept an apartment in Duesseldorf.

Duesseldorf prosecutors said the evidence found in the two homes “backs up the suspicion” that Lubitz “hid his illness from his employer and his colleagues”.

They said they had not found anything pointing to a “political or religious” motive.

According to Bild, the Airbus captain tried using an axe to break through the armoured door.

The tragedy has prompted a shake-up of safety rules, with several airlines announcing a new policy requiring there always be two people in the cockpit and the UN world aviation body stressing that all pilots must have regular mental and physical check-ups.

German Chancellor Angela Merkel said the findings about Lubitz added an “absolutely unimaginable dimension” to the tragedy, in which most victims were German and Spanish nationals.

Among the dead were two Australians, Melbourne nurse Carol Friday and her son Greig.

In the northwestern German town of Haltern, which lost 16 students and two teachers who were returning from a school exchange, the revelations prompted shock and rage.

The principal of the school, Ulrich Wessel, said “what makes all of us so angry (is) that a suicide can lead to the deaths of 149 other people.”

Meanwhile in Montabaur, Mayor Edmund Schaaf urged reporters to show restraint with Lubitz’s parents, a banker and a church organist, who live in a handsome home on a leafy, quiet street.

“Regardless of whether the accusations against the co-pilot are true, we sympathise with his family and ask the media to be considerate,” he said.

Recovery operations at the crash site are ongoing, with French officials trying to find body parts and evidence. A second black box flight data recorder has not yet been recovered.