Thought I'd put in my 2 cents worth on a couple of items from my first hand experience, not just pure amateur speculation which tends to attract emotionally driven comments. Firstly, on loose items. I've flown over 100 hrs aerobatics, competition sequences, low level & the like in high performance GA machines. On one particular occasion, with a paying passenger on a joyflight, while inverted(straight & level), a foreign object landed on the canopy, originating from who knows where. As I was holding the aircraft steady, I had to ask my guest to retrieve the item for me, as I only had 2 hands, & even if I had a third, it was out of reach. This item was a tool, probably left over from another firm's maintenance on the aircraft. Had this item fallen on the floor(which is exposed like the Yak) it could have made it's way into the tail, potentially jamming the rudder & elevator. This item could not be seen before flight, as the cockpit is basic & exposed, like most aerobatic aircraft. I'm under no illusion to the seriousness of finding loose items in the plane. The dismissive comments regarding loose items is from the emotional, uneducated or the inexperienced among posters. However, unfortunately, this does not condone the fact that the pilot flying did not hold the appropriate qualifications at the time. Hence blame & suspicion will be directed in one direction. This damages the reputations those in our industry, also, if by chance it was a mechanical problem(obstruction or other), another event may occur in the future. I'm not saying one way or the other, just giving some facts.
Unless the actual cause, beyond doubt is known, we all need to observe ALL possible contributing factors. It's a pity in this safety driven era, the authorities couldn't raise the wreck for proper examination to once & for all put this thing to rest. Affordable safety, I'm sure.