Andreas Lubitz, the Germanwings co-pilot suspected of deliberately crashing an aircraft in southern France earlier this week, hid details of an existing mental illness from employers.
Submissions from German prosecutors state they do not know what condition Lubitz suffered from, but media report suggested he suffered depression and required ongoing assessment.
German officials revealed they found torn-up sick notes in his home, including one covering the day of the crash.
Prosecutors also revealed there seemed to be no evidence of a political or religious motive to his actions.
No suicide note was found following a search of his residence.
Lubitz and 149 passengers and crew died when Germanwings flight 4U 9525 crashed in the French Alps on Tuesday.
Data from the voice recorder recovered from the crash site suggest Lubitz purposely started a descent as the pilot was locked out of the cockpit.