Germanwings co-pilot Andreas Lubitz apparently hid an illness from his employers. There is evidence that, for medical reasons, he should have been kept off work on the day he allegedly crashed the plane.

German prosecutors are trying to figure it out why Lubitz might have locked the captain out of the cockpit and deliberately crashed the Airbus A320to kill 150 people on Tuesday. Lubitz’s houses in Duesseldorf and Montabaur were searched. Officials discovered documents which indicated that the co-pilot had "an existing illness and appropriate medical treatment."

Ralf Herrenbrueck, however, said that there was no suicide note. The spokesman for the Duesseldorf prosecutors' office said in a statement that there were sick notes on the day of the crash. He said that the notes “support the current preliminary assessment that the deceased hid his illness from his employer and colleagues."

Employees in Germany typically use such notes to excuse themselves from work on a given day. These notes are issued for minor illnesses as well. Employers receive them from workers. Doctors are committed to follow medical secrecy with the exception of the cases when a patient explicitly admits to carry out an act of violence.

Lubitz’s neuropsychologist advised him not to go to work for a period which included the day of the crash. However, he apparently ignored the advice and was said to be eventually responsible for killing 150 people. Prosecutors, on the other hand, did not specify what kind of illness Lubitz might have been suffering from. However, German media claimed on Friday that he had been suffering from depression.

German medical experts say that the airline industry depends heavily on pilots to disclose any serious physical or psychological issues they may be suffering from. Even though it is mandatory to have regular medical tests, employees still trust the honesty of their employees. It is the employees who inform the airline when they are incapable of flying. Several companies like Germanwings reward their employees in return by not punishing them.

While Lubitz apparently kept his depression a secret, there is no evidence that he crashed the plane out of fear of having been declared unfit to fly. However, many believe that it can be a reasonable explanation.

Contact the writer: s.mukhopadhyay@ibtimes.com.au