I'm of the view we are down to one of two options, either an extraordinary event which has not been managed well or perhaps was not possible to manage well.
OR
A Deliberate Act, and I don't believe for a minute the flight crew had anything knowingly to do with that, I'm thinking a lone perpetrator, either an employee or a very good friend of the Captain, someone who could be trusted and invited into the flight deck, a good friendship unsuspectingly established over a period of time, a friendship which was no coincidence.