The co-pilot who crashed Germanwings Flight 9525 researched how to get hold of deadly drugs and the possibility of a living will, it has been claimed.

Duesseldorf prosecutor Christoph Kumpa confirmed a report in German daily Sueddeutsche Zeitung that Andreas Lubitz searched the Internet in March for ways of getting hold of potassium cyanide, valium and lethal combinations of medicines.

He also searched for the term "living will" on the afternoon of March 23, the day before the crash.

A living will spells out a patient's wishes for medical care if he is unable to communicate with doctors.

Prosecutors say Lubitz locked his captain out of the cockpit and deliberately crashed the Airbus A320 into a mountainside during a flight from Barcelona to Duesseldorf, killing all 150 people on board.

A key source of evidence has been the browsing history on a tablet computer found at the 27-year-old's apartment, and prosecutors previously have said that he spent time online researching suicide methods and cockpit door security in the week before the crash.

Prosecutors in both Germany and France are investigating the crash. On Thursday, Marseille prosecutor Brice Robin said information from Lubitz's tablet showed he had also investigated vision problems, and "feared going blind", which would have ended his aviation career.

Lubitz, who had a history of depression, had seven medical appointments in the month before the crash, including three with a psychiatrist, and had taken eight sick days off work, Mr Robin said. Some of the doctors felt Lubitz was psychologically unstable, and some felt he was unfit to fly, but did not report that information to anyone because of medical secrecy laws, he added.

He added that it wasn't yet clear if the vision problems were real or imagined.