If it was a hijacking, and there is a real possibility of that. Almost any trained terrorist know about all the "secret codes" and techniques available to the pilots.
In a moment of duress, putting in the hijack code is the last thing i am worried about. Yes it is important, but fighting for my life probably will come first
If this was terrorism, I know many have said “Well how come no one has claimed responsibility” maybe there is a reason for that..maybe they have a new way of bringing down planes but they don’t want to reveal it yet because there would be even more added security..remember that warning about explosives in toothpaste, or water bottles..or maybe this was an inside job, the baggage handler, they have to investigate everyone