Obviously everyone feels for the families involved, but if the FO was depressed, thats very different to a rational person deciding to crash a plane.
Not it is not. 100% not. If your daughter has just been murdered, it matters not if the murderer was sane or mad - your daughter is still dead. And the murderer is still evil.
The only difference with the madman, is there may well be secondary culpability. If the madman was supposed to be locked up, and some ass of a do-gooder let him out, then a large part of the blame resides with the supposedly sane person who made the insane decision. And that is why a thorough investigation is necessary here. If there is secondary culpability we need to root it out and expose it - especially if evil has been committed in the name of being nice.