Hi Brian
Peter Garrison's comment is only valid for "normal" flying. Ziggy's turn was not what you would see in the circuit being practiced by students and involved a rapid change of heading out of the wind. Dennis mentioned IAS dropping close to zero during his shows, or at least below transition, resulting in insufficient lift to overcome the rate of descent. At least he had sufficient height to recover. It appears this happened to Ziggy but he was unfortunately too low to escape. My example has similarities and is based on experience. I believe Dennis' theory as to the cause of the accident to be reasonable, insufficient airspeed and height for a high rate of turn out of the wind.
"There, but for the grace of God, go I." RIP