Hangman By Michael Slade

The game begins in Seattle, where a hanged woman is found with one leg missing. Then, in Vancouver, a corpse is found with both legs missing. The clue that binds these horrific crimes together is a game of "Hangman" crudely drawn at each location--painted in the victim's blood.

The victims, it seems, were jurors on a controversial case years ago, in which a man was sentenced to death--by hanging. Two cops on both sides of the border--Canadian detective Zinc Chandler and American detective Maddy Thorne--are up against a killer whose every move means death. To stop him, they must solve the riddle of the hangman--before the madman makes his final, murderous move...and wins the game.
 
- Goodreads Summary