The co-pilot of the Germanwings plane crash, Andreas Lubitz, told his flight training school about a previous bout of depression, Lufthansa has said.
The airline revealed last week Lubitz had taken a break from training, but refused to say why.
In a statement it said it had now shared documents with prosecutors, including emails from 2009.
They show Lubitz told his flight instructors “about a previous episode of severe depression”.
A recording from the cockpit of the aircraft suggests the 27-year-old deliberately caused the disaster last Tuesday, which killed 150 people.
Lufthansa CEO Carsten Spohr previously said that the company was not aware of anything that could have driven the co-pilot to crash the Airbus A320.
“He was 100% fit to fly without any restrictions or conditions,” he told reporters.
Lubitz resumed training with the airline in 2009 following his break and had passed all medical tests, according to the company.
He eventually completed his training and started working with Lufthansa subsidiary Germanwings in 2013.
German prosecutors said on Monday that Lubitz had received treatment for “suicidal tendencies”.
But Lufthansa said his medical records were subject to doctor-patient confidentiality and it had no knowledge of their contents.
Meanwhile the company has set aside an additional $300m (€280m; £200m) to cover possible costs arising from the crash.
The money is separate from the $54,250 available to the relatives of each passenger to cover short-term expenses.
Airlines are obliged to compensate relatives for proven damages of up to a limit of about $157,000 – regardless of what caused the crash – but higher compensation is possible if an airline is held liable.
None of the victims were found intact after the plane’s 700kph (430mph) impact, but different strands of DNA have been identified at the site.
French President Francois Hollande said on Tuesday that all 150 victims would be identified by the end of the week.
Speaking at a joint news conference with German Chancellor Angela Merkel in Berlin, Mr Hollande said “exceptional scientific work” had been carried out by the recovery team.
Andreas Lubitz: Germanwings co-pilot
- Started training in 2008, at Bremen and Arizona. Training was interrupted for some months – but he later passed all tests and was deemed fit to fly
- Working as co-pilot, or first officer, since 2013. Appeared pleased with his job
- Lived in town of Montabaur, near Frankfurt, reportedly with his parents. Kept a flat in Duesseldorf and had many friends
- Facebook profile suggests the active lifestyle of a keen runner, with an interest in pop music