Andreas Lubitz, the 27-year-old co-pilot who deliberately crashed Germanwings Flight 4U9525 into the French Alps on March 24, killing all 150 people on board, contacted dozens of doctors before the crash, a state prosecutor told the Associated Press.
Lubitz received therapy for suicidal thoughts before he became a pilot. He was also treated for depression during his training.
The search for doctors indicates he was seeking medical advice about an undisclosed condition, the AP reported.
Brice Robin, the Marseille prosecutor investigating the crash, did not respond to questions on Lubitz' symptoms.
In 2009, Lubitz told Lufthansa, the parent company of Germanwings, that he had suspended his pilot training for several months because of a "severe depressive episode."
So far, the investigation has revealed that Lubitz researched suicide methods and cockpit door security in the days before the crash. He also tore up a doctor's note excusing him from work on the day of the crash of the flight from Barcelona to Düsseldorf.
Victims' families recently expressed anger and frustration in the delays in handing over the remains of their loved ones from the wreckage of the crash.
On Wednesday, Lufthansa informed relatives in 17 countries that the returns of the victims had been "temporarily interrupted" because of a bureaucratic mistake in France, the New York Times reported.