Murder Can Be Fun — Fredric Brown

A novel about an ex-reporter who, disenchanted with his career writing a radio soap opera, looks to create a new show, dubbed "Murder Can Be Fun," and change genres. Things get dicey when killings happen, using our hero's unpublished scripts as a template.

To Bill Tracy, radio script writer and one-time newspaperman, the most incredible thing about the Santa Claus murder was that he himself had planned it! Pure coincidence could hardly account for the fact that the murder had been committed exactly as Tracey had written it for a proposed radio mystery - which he had never shown to anyone.
When the killer transforms another, and still another, of Tracy's scripts to gruesome reality, Tracy has to think fast and act faster to prevent the police from pinning the murder on him.

This book was originally published in 1951 and is also known as "A Plot for Murder."