Andreas Lubitz
Andreas Lubitz Reuters

The co-pilot suspected of deliberately crashing the Germanwings jet in the French Alps had researched suicide methods and the security of cockpit doors, German prosecutors said Thursday, according to the BBC.

Internet searches from the week before the crash were found on the tablet computer used by the co-pilot, Andreas Lubitz. According to the prosecutors, the searches made on the tablet found in Lubitz's Duesseldorf flat included "ways to commit suicide" and "cockpit doors and their security provisions".

"He concerned himself on one hand with medical treatment methods, on the other hand with types and ways of going about a suicide,” said a spokesman, Ralf Herrenbrueck.

"In addition, on at least one day he concerned himself with search terms about cockpit doors and their security precautions.''

Prosecutors did not disclose the individual search terms in the browser history but said personal correspondence supported the conclusion Lubitz used the device in the period from March16 to 23.

Lubitz, 27, had been deemed fit to fly by his employers at Germanwings, a subsidiary of Lufthansa.

This week, investigators revealed he had received treatment for "suicidal tendencies." Several days later, Lufthansa admitted that it was in fact aware that Lubitz was suffering from a severe mental illness - but that it allowed him to fly nonetheless.

According to the company, which owns Germanwings, in 2009 Lubitz contacted his flying school to alert them of "a previous episode of mental depression."

The astonishing admission represents an embarrassing climbdown from claims by Lufthansa CEO Carsten Spoh that the 27-year-old German had been cleared as "100 percent fit to fly without caveats", as the company rushed to avoid responsibility in the immediate aftermath of Lubitz's murderous act.

Skepticism over the company's claims that it didn't know about Lubitz's mental health problems surfaced near the start of the investigation, when prosecutors found several torn-up sick notes in his house. At the time, however, it was claimed he had hidden the evidence from his employers.