For those suggesting the plane might have "shadowed" another to avoid radar...
Regardless of who did it, this appears very carefully planned. Would the culprit or culprits count on that other plane being where it was supposed to be? To me, too big a chance that the other flight might be delayed - then the whole plan falls apart.
The only way I could possibly see it working would be if the pilot of the shadowed aircraft was in on the plot, and that seems exceeding unlikely.