Rules of Prologue/Epilogue?

Hey guys and gals,

I was curious on your opinions of having a prologue/epilogue in a story. For example, my opening paragraph introduces a police officer who will not be relevant to the rest of the story(that I know of). It follows his day until he comes upon a car accident where we meet the protagonist at the very end of the chapter/prologue. Is this more of a style choice or is there protocol one must follow when dealing with a prologue? Would it be less confusing to the reader if I simply made it the first chapter?

Thanks lads for any opinions.