Legion

1983 Simon Schuster hardcover, William Peter Blatty. One by one the bizarre murders frustrate and torment Lt. Kinderman, the homicide detective from The Exorcist. A boy, crucified; a priest, decapitated; another priest slain; a nurse, slaughtered — all bear the Zodiac mark of the Gemini Killer. BUT ... the Gemini Killer has been dead for 12 years — Lt. Kinderman stalks the brutal and elusive killer down the dark streets. Until, finally, in desperation he dares to cross the boundary that separates the living from the dead. - Goodreads