The co-pilot blamed for deliberately crashing Germanwings flight 4U9525 into the French Alps and killing all 150 people on board took time off from training because he was depressed, German media report.

Andreas Lubitz, 27, stopped training for six months because of "burnout syndrome" or "depression" in 2009, former classmates told Der Spiegel weekly.

Matthias Gebauer, Der Spiegel’s chief correspondent, tweeted: "Schoolmates of co-pilot who crashed tell German reporters he took six-month break from flight training in 2009 due to burnout-syndrome”.

According to German daily Bild, the 27-year-old had been the recipient of a “specific and regular medical treatment” ever since his bout of depression in 2009.

Bild said psychologists were due to examine his medical record and documents provided by the airline on Friday.

Carsten Spohr, CEO of Germanwings’ parent company Lufthansa, had earlier told reporters that Lubitz took a "several-month gap" six years ago.

However, he said: "I am not able to state the reasons why he took the break."

Lubitz later resumed training and passed all his tests, including psychological and medical exams, Spohr said, adding that the co-pilot was deemed “100 percent fit to fly without any restrictions”.

“We can only speculate what might have been the motivation of the co-pilot," Spohr added. "In our worst nightmares we could not have imagined that this kind of tragedy could happen to us".

‘Happy’ with Germanwings job

Authorities are still at a loss to explain why Lubitz appeared to have taken sole control of the plane after locking the pilot out of the cockpit then deliberately forcing the aircraft into a fatal descent.

Lubitz, who lived with his parents in the small western German town of Montabour, qualified as a pilot at the Lufthansa training centre in Bremen, and began flying for the airline’s low-cost subsidiary, Germanwings, shortly after completing the course in 2013.

At the time of the accident, Lubitz had accumulated 630 hours of flight experience, according to a Lufthansa spokeswoman.

An avid runner who often took part in local races, Lubitz was also registered as a member of a private flight club, LSC Westerwald, in Montabour.

Peter Ruecker, a fellow club member, described Lubitz as upbeat.

"He was happy he had the job with Germanwings and he was doing well,'' Ruecker told the Associated Press. “He was very happy. He gave off a good feeling.”

A photo on Lubitz’s Facebook page, which was later taken down, shows a smiling young man posing in front of San Francisco’s Golden Gate Bridge.

What do we know about Germanwings co-pilot Andreas Lubitz?

On Friday, German police searched Lubitz's home looking for a possible motive for the air crash.

Marseille prosecutor Brice Robin, who is in charge of the investigation into the crash, said that there was no reason to suspect a terror attack. Germany’s interior ministry later echoed Robin’s comments, saying that there was so far no indication that Lubitz had a "terrorist background".

Robin said that Lubitz’s family had arrived in France for a tribute to the crash victims, but that they were being kept apart from the other families.

(FRANCE 24 with AFP,)