We have been musing at work that if this guy had been treated for suicidal tendencies and had blurred vision how his employer wouldn't know this? 

I believed (and believe it should be if it isn't) that a pilots medical notes are copied to their employer, and it defies belief that anyone treated for suicidal tendencies would ever ever ever been allowed to pilot a passenger vehicle of that size.

For the same reason I believe that a criminal conviction should prevent you from ever owning a gun of any type. 

This should have been preventable to some degree, or mitigated somewhat.