Ah, the enigmatic Zodiac Killer. True story: the serial murderer was never captured, but the mystery of his identity and the torment he caused detectives and one sleuth-y writer are showcased in David Fincher's haunting detective thriller 'Zodiac,' which posits at least one very strong suspect who was never apprehended. We can never be sure exactly who the killer was, but sometimes it's that which is intangible and impossible to identify that is the most terrifying.