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 murderer is always lurking along the perimeter of the tale but not too far out of sight, then the revelation of their identity can be a stunning surprise for the reader. But by planting that person as one of the central suspects, I can also give the reader the fun of playing detective along with Dalton Lee.
How do YOU like your murderer served up? On the side, as an unexpected garnish ? Or as one of several delicious morsels on the main dinner plate?