When to introduce the murderer…

As I begin preliminary work this week on the third book in the “Murder Becomes” series, I am reminded of one of the biggest challenges I face – where in the book to introduce the murderer.

Should it be very near the beginning, when the reader least expects it and has lots of time throughout the book to forget them? Or should it be deeper within the book, right as the intrigue is kicking into high gear?

I also have to consider how central to the main story the murderer should be. If the murder...