I thought he died because of bad weather and his lack of skills in flying that type of plane in bad weather.
I do remember Bush43 allowing The Swimmer's wishes to prevail, and had the autopsy cancelled.
Find the AOPA synopsis of his flight. I was a member at the time and read it and I was almost sick to my stomach. No I am not instrument rated, but you get the sense he got spatially disorientated and didn't believe his instruments and went with the seat of his pants feel. The tell was the rapid speed increase before impact. IMHO that is I don't know up from down and pulled back on the stick when his was in a deep left hand spiral if my memory is correct. He was probably almost inverted in a dive.
Any of this other conspiracy drivel is an insult to all of us who lost friends while PIC and have read their NTSB reports. These accidents are always a seris of bad decisions that end up in a less than optimal outcome, unless is is an exogenous event, aka engine failure, control system failure or structural failure, the last being very rare.
He could have asked his instructor to come that day, or decided not to go, or called a Maday or let a tower know he was need of flight assistance because he was temporary disoriented. Boston or Fall River would have given their eye teeth to help him if they knew it was him IMHO...