LH's CEO Spohr is probably right, there is no way to make sure something like this will never happen again.
Pilot associations do not seem to dare reject the two-person-rule under the current circumstances, although we all know that the rule is problematic for a number of reasons. However, the two-person-rule is welcomed by the airlines as a cheap and immediate measure that seems to make the flying public feel safer. This will change after the first crash due to a recently hired FA knocking out the remaining pilot from behind, locking the door and flying the plane into ground or a skyscraper.
