I believe this was a loss of control accident. The pilot was trying to avoid weather ahead and began a right turn to avoid the weather. As you read the NTSB report at 1233:37 he began a right decending turn. This turn continued and after 1234:01 it plunged down to 10700 feet. The turn was probably tight and the descent was fast. Also speed was reduced and then increased. This may have lead to a stall and then a right spiral downward. To recover from this flight condition you have to use the proper flight controls. In a downward spiral pulling up on the controls to recover or maintain level will exceed the structural limits of the aircraft and it may break apart by loosing a wing or control surface. The proper recovery is go to wings level, contol airspeed and do a smooth level off to maintain altitude. Doing it wrong can cost you. Each airplane has what is called a maneuvering spreed. This is the speed where you can do a full deflection of the flight controls without exceeding the structural limits of the airframe. In a case like this it is a very important speed limit.
That said, I have to say I have flown into a thunderstorm, dumb move on my part, and lost control of my plane. It does happen quickly. I went from 11,000 to 15000 in a flash and the instuments showed I was out of control. Recovery was in the clouds and by instruments and I turned back to where I came from cause that was where the good weather was. Then I informed ATC what had happened. I landed at a nearby airport to wait the weather out. I also checked the airplane to see if anything was bent and any rivets popped. I have stayed clear of that kind of weather since.
When I read stories like these I alway remember that encounter and remember how fast things happen.
Here is a video of a PC 12 doing stall tests.
Stall Tests