Co-pilot researched cockpit doors, suicide

German prosecutors say the co-pilot suspected of deliberately crashing a Germanwings plane in the French Alps had searched online for information about suicide and cockpit doors in the week before the disaster.

A tablet computer which prosecutors said was used by Andreas Lubitz was found in a search of a flat he used in Duesseldorf, the prosecutor's office in the western city said in a statement.

"The browser history wasn't erased, in particular the search terms called up on this device in the period from March 16 to March 23 were able to be retraced," it said on Thursday.

"The user focused on the one hand on medical treatment methods, in addition to informing himself about ways to commit suicide," it added.

On at least one day, Lubitz had also spent several minutes on search terms about "cockpit doors and their security provisions", the prosecutor's office said, adding it would not release the individual search terms.

Investigators believe Lubitz, 27, locked his captain out of the cockpit during the Barcelona to Duesseldorf flight on March 24 and deliberately flew the plane into a mountain, killing himself and the other 149 people on board.

German prosecutors had said on Monday that the co-pilot was treated for suicidal tendencies "several years ago", before he received his pilot's licence.

Lufthansa, which owns the low-cost Germanwings airline, said the following day that Lubitz had informed the carrier in 2009 that he had previously suffered from severe depression.

German daily Bild also reported that Lubitz told doctors he saw in the weeks before the crash, that he was written off sick and not flying at the time.

Citing files obtained by investigators, it said that Lubitz had been involved in a car accident in late 2014 in which the airbag opened and injured him. He said he was suffering from trauma and poor vision.

The records also showed that Lubitz told his doctors he was on anti-depressants and Lorazepam, a mild tranquilliser used to treat anxiety.