BERLIN 

he co-pilot of the Germanwings plane which crashed in the French Alps killing all 150 people on board was not capable of working on the day of the tragedy, torn-up medical certificates found in his house have revealed, according to German prosecutors.

Chief Public Prosecutor Ralf Herrenbrueck said on Friday that police had found several medical certificates showing Andreas Lubitz, who is believed to have deliberately flown flight 4U 9525 into mountains in southern France on Tuesday, was undergoing medical treatment, but he had kept the fact secret from his employers.

Herrenbrueck said: "The torn-up medical certificates found in his home, which were up-to-date and also covered the date of the incident, support the preliminary assumption that the deceased (co-pilot) had kept his illness secret from his employer and his professional environment."

He said no suicide note nor letter indicating a political or religious background was found during the searches in the co-pilot’s house in the northwestern city of Duesseldorf and at his parents' house in the town of Montabaur.

Germanwings said in a written statement on Friday that the co-pilot had not forwarded a request for sick leave request on the day of the crash.

“Germanwings declares that a sick note for this day was not submitted to the company,” it said.

But the company did not comment on the speculation in German media that the employers of the co-pilot knew that the 27-year-old co-pilot had psychological problems.

German daily Bild reported on Friday that the co-pilot had suffered from depression in the past and had to interrupt his flight training with Lufthansa, the parent company of Germanwings, in 2009.

Training interrupted

Bild reported that the psychological problems of the co-pilot were mentioned in the personnel files of Lufthansa.

Lufthansa’s Chief Executive Officer Carsten Spohr had told reporters on Thursday that Lubitz had to interrupt his training in the past, but declined to comment on the reasons.

The French prosecutor Brice Robin, who is responsible for the crash investigation, said at a press conference in Marseille on Thursday that the co-pilot had deliberately taken the plane down.

"The co-pilot intentionally kept the pilot outside the cockpit and took the Germanwings plane into a dive. The intention was to destroy this plane,” he said.

Deadly crash

The Germanwings Airbus 320 was en route from Barcelona, Spain, to Dusseldorf in Germany, when it went down on Tuesday before 11 a.m. local time (10:00 GMT) after an eight-minute descent, killing 144 passengers and six crew members on board.

The majority of the victims were German and Spanish.

The air disaster is one of the most tragic incidents in recent German aviation history, and the first deadly crash of a Germanwings plane since the low-budget airline was founded by Germany’s largest airline, Lufthansa, in 2002.

The crash was also the first on French soil since July 25, 2000, when an Air France Concorde crashed into a hotel in Gonesse in the Val-d'Oise, shortly after taking off from Roissy-CDG airport, killing 13 German passengers and crew members, along with four others on the ground.