Sadly, most of the reports jive with a flutter event. While it is just speculation, the scenario that eyewitnesses have been describing does seem to make sense.
A flutter event is really, really violent. I have been on flutter test flights, that thankfully proved we did not have flutter. A fellow I know was on a business jet that experienced elevator flutter. The control wheel was whipped out of his hand, and the control columns moved back and forth so fast that it became a blur which neither he or the pilot could grab. Eventually the control system connection between the elevators and the control column failed, causing the dynamics to change enough that the flutter stopped. Of course they had no elevator control.
If this plane had just passed another plane (as has been reported) the wake off the other plane could have started the flutter. This would have undoubtedly ripped the stick out of the pilot’s hand. With nothing controlling the ailerons (because he is not holding the stick) a barrel roll as several people have reported is completely possible. He more than likely would have tried to reduce engine power, and it is likely the elevator control system failed due to the overload. This would have let him have rudder and aileron control, but with the aircraft pointed nearly straight down at high speed and low altitude. Rudder and aileron might have let him change his trajectory some (as people have also reported)but at that attitude and altitude, there really was really no chance.
Of course that is just speculation at this point. Unfortunately with the level of aircraft destruction that occurred, unless there is some better photographic evidence we may never know.