If we want to find the most likely cause of the plane going missing, a sensible question might be:
In what situation would this be the best location to "disappear" a large jet?
For example: if you wanted to steal it, intact, is there anywhere else in the world where the combination of remoteness, lack of radar coverage, getting "your" aircrew on board and easy (without much technology) landing and concealment would offer a greater chance of success? If there are places that would make the theft easier to get away with, then maybe it would rule out that particular possibility for the disappearance.
Just go through the list of possibilites until this location bubbles up to the top, then assume you've got the reason - search accordingly.