A bunch of people reported hearing a sharp crack before he spun in. I wonder if an elevator control cable broke under the tension?
Assuming the engine was operating on the jet I seriously doubt even the pilot would hear a control cable parting even if it was under his seat if the jet was even equipped with cables rather than a hydraulic control system.
I wonder why he didn't punch out once the bird got low. It is possible he wasn't conscious at the time or otherwise incapacitated.