My wife getting scared

Paul Tomblin writes:

The problem with that approach is that after the DE guy died, that worked
because Rochester aviation's dirty little secret was that he was a known
corner-cutter and risk taker. But when the other two died, I had to admit
that I've flown with one of them a couple of times and I couldn't fault
anything he did. He seemed to me careful and methodical and professional.

What was the actual cause of his accident?