Documents found in the apartment of Germanwings Flight 9525 co-pilot Andreas Lubitz indicate he had an illness he kept “secret from his employer and his professional environment,” official says.

Investigators found a medical leave note from a doctor issued for the co-pilot that included the day of the crash, the Dusseldorf public prosecutor’s office said.

The prosecutor’s office did not say if the medical leave note related to a physical or a mental health issue but said the co-pilot appeared to have been under treatment by a doctor for some time.

Investigators added that no goodbye letter, and no evidence of political or religious motivation was found, the prosecutor’s office said.

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