Lubitz may have planned his atrocity years ago, perhaps during the long break in his training. Society doesn't have a good way to ferret out those people without a conscience. Psychologists need to develop those tests. "if an instructor gives you a poor grade on a test, what would you want to do to the instructor if you could get away with it?"
A good first step would to give tests to pilots that would try to determine if pilots have a functioning conscience.
Any objection from the pilots here?