At what point does a victim of a crime have to pursue criminal charges?

Does it have to be the victim or merely a witness , since the affidavit apparently is not necessary if the officer witnesses the crime?

Has to be the victim in my state.

It might be worth mentioning here that Commonwealth law is more like a hedgerow gone to pot, or a garden given over to weeds, than a planned and maintained botanical garden: There’s a structure there, somewhere, underneath all of the undisciplined organic growth and millennia of cow paths worn into the landscape, but at this point trying to reveal it would destroy the character of the laws.

America imported the Common Law, that prized family heirloom, but we made a cleaner break, so we also got to write more of our laws from a clean slate. Starting with a Constitution we can actually point to.