As the current thinking is moving away from an accident to a willful act, all the possible scenarios have one thing in common: they require a good deal of planning and preparation with nothing left to chance, and the kind of impeccable timing that one can see in a Mission: Impossible movie. Such preparation needs both time and money, and likely involved a number of people. It is very clear that any such planning must have involved this particular flight, as a number of key parameters (eg. takeoff time, initial flight path, fuel endurance, etc.) are unique to this flight only. I think it is also no coincidence that a moonless sky was chosen.
The key emerging question is why this particular flight would have been chosen as the target of such a massive investment and effort. I can think of several countries in the region where security procedures are much more lax (speaking of experience, will say no more), I can think of several airports on the border of oceanic zones where it is much easier to slip away from primary radar, etc.
Clearly understanding the motives is the key to the puzzle, as it is drifting away from being a purely aviation matter to something of much broader implications.