Dr Lepastier said Lubitz's initial severe depressive episode "could have been the first manifestation of schizophrenia, which often first strikes in one's early twenties".
"Patients can then feel they have fully recovered only to discover years later that their condition is worsening and they require treatment that could be very long. It is at this stage that the temptation to commit suicide is greatest. What we don't know is if Lubitz had been told he might require hospitalisation and realised his pilot career was well and truly over." German prosecutors this week revealed that Lubitz had conducted Internet research on "cockpit doors" and "suicide" right before the crash.
Dr Lepastier said there was a "documented desire" among schizophrenics with suicidal tendencies to "end their life by breaking their body into pieces – as was the case here".
He added that along with the drug's side effects of visual impairment, drowsiness and impotence, "one is also cut off from one's own emotions and in moments of stress, can make entirely the wrong decisions".
Asked whether he would have been aware he was committing mass murder, Dr Lepastier said "probably not".
"Melancholic or deliriously depressed people are so narcissistic that others don't count in their mind. There may well have been no real desire to kill others; rather one can say he forgot about everyone else and in the end nothing counted except his own situation." "That said, one should never forget that a suicide is in fact a murder committed against oneself."