I suppose the big problem in how to investigate/analyse this comes from the basic problem that no-one knows what sort of event was planned, or whether the plan was successfully carried out.
I expect that the intelligence effort (which won't be made public) will be looking amongst other things for 'chatter' to see if thy can discover the intended purpose - and as it's been made public previously that planning for terrorist events takes years, that is a lot of material to review.
But if suicide by pilot, then there would be no noticeable planning.
Terrorists often leave a video "will" explaining thier actions, released onto the Internet shortly after the event. If this event has not gone as plan (say if brave pilots managed to ditch the plane, or if erratic flying by inexperienced hijacker led to a critical mistake); then perhaps you delay release (perhaps simply relishing the tying up a huge number of international experts).
On the 'preprogrammed change of course' theory - did anyone say how they know (there must be a version not on the plane?). And would this be consistent with flying to avoid known radar?