- The murder must occur within the first 3 chapters.
Anyone who picks up a murder mystery is expecting, well, a murder to occur. Until that happens, the reader is just sort of left in suspended animation, waiting for something to happen. I’ve read a lot of mysteries where the actual murder took place before the book began, and the corpse is found in chapter one. I’ve also read books where the first two or three chapters are setting-up suspects and motivations, then the murder occurs. Personally, I like to start off with the murder occurring in chapter one, then introduce the sleuth in chapter two.
- The murderer must be present within the first 3 chapters.
You’re not playing fair if the character who committed the murder is introduced too late in the book to be a viable suspect. He (or she) should be present from the very beginning. A strong mystery writer will introduce the character, but not draw attention to him.
Really, you can’t go wrong as long as a body is found that kicks-off the investigation within the first three chapters. The murder and the questions that follow are what hook your reader. Obviously, you want to do that as quickly as possible.