*My guess is he probably attempted too steep of a turn and
had no idea he was in any danger of spacial disorientation because he didn't
recognize that he was in instrument conditions. *Unfortunately it's a common
mistake for low time pilots and lots of them kill themselves that way.

He was tracking right towards the airport, I'd assume on a/p. My guess
is he chose to hand fly and started his descent and lost it. There was
zero need for a turn at the place of the accident. A wings level
descent from 5500 feet to pattern altitude in 15 miles is what was
needed, so he needed to lose 4500 feet or so in 7 or 8 minutes. I
would rather go down slower, but less than 1000 fpm is not in itself
bad. Any turn other than course correction was not needed.