glojo, I must respond to your "nothing has changed". The JP crash I referred to was not fatal, perhaps I should have made that clear. Your list of offences it was mandatory for the Civil Authorities to investigate was true in my time, also. That is why I chose my hypothetical crimes as I did. Sabotage is not on your list, murder is.
Your 3rd para "not going to speculate on why the civ police were "called in" is missing the point. They weren't "called in" they were acting in accordance with "police primacy", which is what this discussion is about.