My point was not about the fine detail of legal process: which I deliberately avoided discussing, but that unless something is utterly and blatantly criminal, then that is not AAIB's judgement to make and indeed, they would be grossly failing in their duties if they tried to make that judgement.
Criminality is the Police's judgement to make, insofar as they make decisions about whether to put a case to CPS or other agencies for possible prosecution. It is not the Police's judgement to make whether anybody should receive recommendations about preventing a future accident - they are not competent to make such a judgement.
Hence the different approaches, and that the evidence gathered for each needs to be gathered in different ways.
G