If prima facie evidence of wrongdoing, criminal activity, carelessness, malpractice, or indeed the exact opposite exists, it should be made available to investigators, no matter what the original reason for gathering or recording that incident. The very fact that people might modify their behaviour in response to the knowledge that everything they do is being recorded is telling in itself.
It appears that air display organisers and pilots have been playing a bit loose and fast with the rules for quite some years. So long as no one gets hurt and the public get to see an exciting display, its okay, right?
Well, no it isn't. The odds may be a million to one against a serious incident, but sooner or later that chance event happens, and without the additional safety factors built in by the rules, people get hurt. It is always a combination of factors and investigators need to be able to access all the data to arrive at the correct finding. That result may not be "fair", but it should at least be an accurate account of events.