I recall circa '79 or '80 there being a paperback novel in the bookstore titled Halloween. I’m pretty sure this was not the Curtis Richards novelization of the film Halloween because the cover I remember did not reference the film. but it was about a serial killer also. Because of the lack of reference to the film, I was under the impression at the time that the film was loosely based on this book. I doubt that was the case now. But I can’t find anything online about this book. Anyone else remember it?
The cover art I remember had a gravestone, and blonde braids of a girl, the rest of whom was outside the boundary of the art.
The movie Halloween wasn’t based on a book. In 1976, Irwin Yablans and Moustapha Akkad suggested that John Carpenter and Debra Hill make a movie about a psychopath who stalked a babysitter. Carpenter and Hill came up with the script which was then made into the movie Halloween. I can’t find any novel with the name Halloween from about the time period you suggest. There have been some books with that title, but mostly they are nonfiction things about Halloween customs: