I wonder if any criminal charges will be made against the airline.
I've been thinking about this and put my law cap on.
I'm guessing any criminal proceedings would go down the negligence route.
Here is a link to the stages of proving negligence
http://injury.findlaw.com/accident-injury-law/proving-fault-what-is-negligence.html
So it's a no brainer that the airline owed a duty of care to its staff and passengers.
So we go on to stage 2 - Breach
"whether the defendant breached this duty by doing (or not doing something) that a "reasonably prudent person" would do under similar circumstances"
The consequence of the risk also needs to be reasonably foreseeable. I.e. if I stand on a chair with a loose leg is it reasonably foreseeable that the chair will collapse causing me to fall?
So, I'm thinking that there are two main routes which could be bought up.
1. Was it reasonably foreseeable that by not having a "2 person in the cockpit rule" that the plane would be taken over by a rogue crew member... well I would argue no. There is no such law dictating that European planes need to have this rule (although it is best practice in USA to do so) so Lufthansa have not breached any law. There have been very few cases where planes have been overtaken by rogue crew members so there is no past history patterns which would make this forsee able. There are many other reasons why this exact situation is unforseeable (although though some may argue that by not having two people in the cockpit it is reasonably foreseeable that the plane was open to subterfuge/hijacking by others however the implementation of safety devices such as the internal door lock is meant to mitigate against this)
2. Is it reasonably foreseeable that a crew member with a past history of mental health issues could suffer a relapsed flight. Well, this would depend on whether the airline knew the crew mber had suffered from mental health issues previously. If they did know then it would need to be looked into to determine what controls were put in place to mitigate this risk (/termination of contract/regular psych tests/counselling/special protocols put in place). If they weren't aware then no it wasn't foreseeable - if they don't know then they can't do anything about it.
So if they did know and they did not act to mitigate against this then yes they would be found negligent in a nutshell
It seems unclear at the moment whether the airline were or weren't aware of his past mental health history
Just my two cents worth I'm sure many will disagree but happy to discuss!!