Legion - Sequel to the Exorcist

A young boy is found horribly murdered in a mock crucifixion. Is the
murderer the elderly woman who witnessed the crime? A neurologist who
can no longer bear the pain life inflicts on its victims? A psychiatrist
with a macabre sense of humor and a guilty secret? A mysterious
patient, locked in silent isolation in the psychiatric ward?

Lieutenant
Kinderman follows a bewildering trail that links all these people,
confronting a new enigma at every turn even as more murders surface,
with each victim suffering the same dreadful mutilations. Kinderman must
confront the creeping suspicion that there's a connection between these
crimes and another series of murders that took place more than a decade
ago?and supposedly ended with the death of the Gemini Killer.