This reminds me of the initial AF447 thread. Some of the same members also.
Theories we can (almost) 100% eliminate:
1. Explosion (bomb or otherwise) near last known point (loss of transponder). This would have generated large pieces of debris over a large area, and we would have found this by now.
2. Vertical dive into water (suicide or hijacking) near LKP. This would have caused severe fragmentation at impact, and we would almost certainly have a more compact field of debris. Even if the everything sank and was embedded in mud as some suggest, the fuel tanks would have ruptured. There were tons of Jet A on board, and this would have surfaced even if nothing else did. Oil is still coming up from the Arizona. In addition, there would seem little point turning off the transponder.
3. AF447 type of event near LKP. Loss of control, and pilots too busy to make a call. Again, we would have found debris by now.
So the plane is not near LKP, and so the plane flew on without communication.
4. Failure of pressurisation and unrecognised incapacitation of crew? Does not explain transponder.
5. Fire, loss of all electrics and comms, plane continued to fly, but crashed due to disorientation etc. Hard to believe such an event could be so quick and so complete as to prevent a call (even if just ACARS).
That seems to eliminate the "innocent" causes of the plane flying past LKP. We are then left with less innocent causes.
So someone disabled all comms and transponder, and flew the plane some distance from LKP. Could have landed or crashed, but most likely crashed.
Why fly on only to crash? Well terrorists are now less keen to claim responsibility - if the plane can't be found it is hard to be implicated. Plus not knowing what happened is more effective at inciting terror than knowing - and terror would appear to be the only motive if no hostage, no ransom, and no demand.
If it was the pilots flying, there may have been concern about the reputation of family left behind. Plus suicide may have implications on any insurance payout.