Whilst we are speculating, I'd be interested to know whether it was a consistent turn to the left and a consistent spiral dive based on what they have of radar paints.
A gentle spiral dive, ending in a fast one, doesn't sound at all like a loss of control, but more like incapacitation, but they attempted to cover that with the comments on the passenger being as good as qualified for the purposes of identifying a spiral dive as such and being able to fly this aircraft.
I would like to know more about the recorded track as you'd think that with a loss of control due to autopilot of control jamming that there would be erratic altitude and headings recorded and not just a gradual left turn or whatever the report said.
I also don't understand why they didn't call center, given that they were in close contact with them by the sounds of it. That doesn't make sense. Pilot incapacitation would be a culprit, but surely the passenger would have called for assistance? It's not making much sense unless they somehow all became incapacitated.
Surely and I say that surely they would have noticed they were descending into a spiral dive if the auto pilot came off?