If he has indeed relapsed in to some form of depression (or other mental illness) then I can understand the apparently torn up sick note, after years of fighting to recover and then finally doing well, admitting even to yourself that it's come back is an awful situation to be in.
I am also curious as to whether he was on any kind of medication. Even though I live in Germany myself now I haven't seen a doctor here regarding mental issues, I only have however in the UK and given societies stigma towards mental health as a whole I can't see the 2 being worlds apart. I was only ever given antidepressants at my worst, the odd referral that came to nothing but the main thing was 'take these pills and see how you are in a few weeks'. At the 3rd lot I tried the depressed 21 year old I was became hooked on the 'high' from venlafaxine until it just didn't happen anymore and I came down to earth with a massive thud, and, ironically it was whilst taking these pills that should have made me better that I wanted and almost did commit suicide.
Now granted I didn't nearly take another 149 with me at that moment but there were times even driving down the motorway thinking I could just swerve off, that could, had I of done it caused a massive pile up but at no point did I think about that, my only thought was that I just couldn't go on feeling that way anymore, noone really could or wanted to help. When you feel like that everything could be an opportunity or you could plan it down to the final detail, imo his actions if they were to end his life could have been a mere thought once upon a time of how he could do it and then on that day the chance presented itself, I don't think we'll ever know.
I am not justifying any actions (if this was even what the cause was) but I can understand the thoughts that could go through someones mind in that position.
I personally feel if anything should come out of this other than sticking cc in the flight deck when someone needs the loo is that companies and management NEED to somehow be more understanding towards mental illness.
At the same time as I mentioned above I ended up having to tell my employer to not lose my job and that was just awful. (I'll add that I was a pax service agent so no where near as much responsibility but I still had crazy shifts which don't help) My HR manager said 'we all have bad days'
and I got no help or support, in fact they even prevented it so I can totally understand why he would not tell anyone.