DUESSELDORF, Germany — The co-pilot of Germanwings Flight 9525 that crashed into the French Alps last week had received treatment for suicidal tendencies several years ago, prosecutors said Monday.

Duesseldorf prosecutors say co-pilot Andreas Lubitz, 27, had received psychotherapy “with a note about suicidal tendencies” for several years before becoming a pilot.

“In the following period, and until recently, further doctor’s visits took place, resulting in sick notes without any suicidal tendencies or aggression against others being recorded,” prosecutors’ spokesman Ralf Herrenbrueck said in a written statement.

He did not say where this treatment took place. Lubitz trained to be a pilot both in Germany and at the Lufthansa training facility in Phoenix, Arizona.

Authorities believe, based on data from the plane’s cockpit voice recorder, that Lubitz locked his captain out of the cockpit and ignored his pleas to open the door while sending the plane into a fatal descent on what should have been a routine flight.

All 150 people on board were killed when the Airbus A320 plane flying from Barcelona to Duesseldorf slammed into a French mountain on March 24 near the Alpine village of Le Vernet.

The crash has prompted wide-ranging questions about Lubitz’s motivation, his mindset, aviation industry regulations — and in the minds of the flying public, concerns about air travel safety.

Lufthansa, asked whether the airline had been aware of Lubitz’s previous psychotherapy treatment, said only that all medical information is subject to medical confidentiality rules.

Prosecutors said they have so far found no indications in Lubitz’s family, his personal surroundings or in his work environment of any motive that might have prompted his actions. They have not found any sign of a physical illness and have no evidence that he told anyone what he was going to do.

Prosecutors have previously said that, when they searched his home, they found torn-up sick notes from a doctor, one of which would have kept him off work on the day of the crash.

Asked about reports that Lubitz had problems with his vision, Christoph Kumpa, another spokesman for the Duesseldorf investigators, said there was no evidence showing that Lubitz had any physical ailment affecting his sight.