Those were very difficult videos to watch on the news and youtube....
I spoke with a retired racer last night.. He agrees with me that until the experts review all of the video evidence (frame by frame) and do an exhaustive investigation, there's no way to accurately guess at what happened. Flutter is a very strong candidate. My friend raced a P-51D and said that trim tabs sometimes rip away when exposed to extreme loading, so it could a cause or an effect. Either way, GLOC was a real possibility under the loads that Mustang was under (likely around 450 mph initially).
This is a terribly tragic event... We'll have to wait until the NTSB releases a report as to what happened, or probably happened.