Having spent some time working in Germany and also alongside German students, I have to say that Lubitz fits a type. Extremely conscientious (look how he steered the plane so gently down, that the passengers themselves didn't raise the alarm) and utterly efficient.
He had probably decided...
Have read what is in "the Times" this morning. Wouldn't it be logical to make the cockpit area a complete separate unit i.e. with its own toilet facilities? Surely that could be done with no loss of integrity to the plane's fabric. Then it would not be necessary for crews to leave the cockpit...