Lampshaded: "So Bob is the real killer! ...I didn't see that one coming."
Invoked: Officer Bob decides to commit murder because nobody would suspect him, being the lead murder investigator.
Defied: Because Everyone Is a Suspect, Officer Bob's first priority is to prove his innocence in the recent string of murders.
Discussed: "It's always the one you least suspect... least of all the one leading the investigation."
Conversed: "In this new mystery novel it turns out that Bob is the killer, and was hiding it."
Played For Laughs: Two of the leading inspectors make a bet on whether Bob is the killer.
Played For Drama: Alice is traumatized at the revelation that her best friend was the murderer.
Straight: After pursuing the killer throughout the entire story, Officer Bob finds out that he is in fact the killer, and was suffering amnesia.
Exaggerated: The entire police precinct was in on the murders, and somehow they were all unaware of it.
Downplayed: Officer Bob knows that he committed a single murder, but when he finds out that he committed all of them he is shocked.
Justified: Bob is psychologically disturbed and blacked out everything.
Inverted: Charlie believed that he was a serial killer, but all his murders were hallucinations.
Subverted: Officer Bob finds out that he was the killer all along... but when he turns himself in, it's revealed that all the people he killed are still alive, and that he was merely hallucinating that they were dead.
Double Subverted: The cops revealing to Officer Bob that all his victims are still alive was itself a hallucination that Bob created to cope with finding out that he is a murderer.
Parodied: A petite young woman finds out that she is in fact the hulking 6' 9'' killer, who looks nothing like her.