Credentials: Retired military and airline pilot
Working backwards, it appears we have a near vertical dive with some associated breakup. How do we arrive in that position? Imo:
1. Catastrophic mechanical failure in cruise - unlikely
2. Pilot suicide - unlikely, plausible.
3. Terrorist act - unlikely, plausible
4. Gradual stab trim until autopilot gives up and kicks off, followed by departure from controlled flight. Recovery attempt overstresses aircraft. - plausible
5. There are many other ways to depart the aircraft and botch the recovery. - all plausible at this point.
We are going to have to wait and see.