The biggest plot hole (contains spoilers) don't read if you haven't seen

the movie.


You guys probably already know this



The sheriff/prowler: they would have figured out it was him who killed Rosemary at the beginning of the movie. They would have put 2 and 2 together and figured out he was the killer of her and her boyfriend. So, he would never have actually become a sheriff. I'm sure Rosemary's parents knew that she wrote him the letter.

But if that happened, you wouldn't have the movie. Total Hollywood b.s.