^^^ not really possible, if the keypad had malfunctioned you can just call the flightdeck on the interphone and the remaining pilot can automatically or manually open the door for you to get back in.
What is more likely:
- Captain leaves flight deck
- FO has some sort of unexplained medical event rendering him incapacitated
- FO still for some reason while incapacitated initiates a descent without clearance.
- Captain tries to call flightdeck for re-entry and either fails to use the emergency entry code or some mysterious fault prevents it from working.
- Aircraft crashes.
or:
- Captain leaves flight deck.
- FO initiates descent without clearance.
- FO ignores entry requests
- FO puts door into LOCK preventing emergency entry.
- FO sits back and waits to the end calmly as it is almost all over.
Having know someone who did commit suicide, I concur with all the previous comments. Often people who have decided to end it all are calm and happy as they feel it is almost all over, there is no rational thought at this stage.
The prosecuter did NOT rule out suicide just said that the act of taking 150 people with you would not be classified as suicide by him. Mass murder probably.