David Berkowitz

He began murdering people in 1976 and continued for a year before he was caught by the police. The murders were all similar: He would approach his victims at night, shoot them with a .44 revolver, and leave without saying a word. At one of the shootings, he left a disturbing note for the police, which talked about "Father Sam" who "drinks blood" and commands him to "go out and kill."

Berkowitz's real-life father was named Tony, so who was Sam? According to Berkowitz, Sam was the demon who had possessed his neighbor's dog. When Berkowitz was arrested in 1977, he gave a full confession, claiming that the dog spoke to him and told him when to kill someone. Sometimes he called Sam a demon, other times he said that Sam was the spirit of an evil man who had lived 6,000 years ago and had found a conduit through the Labrador retriever living next door. Whether the story was fabricated to grant him an insanity plea at his trial or not, the combination of the macabre note and a demon-possessed dog is enough to send chills up your spine.