14. David "Son of Sam" Berkowitz
Armed with his trusty .44 caliber Bulldog revolver, the Brooklyn-born madman David Berkowitz conducted several shooting attacks throughout New York City from July 1976 through August 1977, leaving six people dead and seven others wounded. Media outlets jumped on Berkowitz's actions as he left numerous letters threatening the NYPD with future killings, and when he was finally apprehended, the "Son of Sam" was sentenced to six consecutive life sentences.
All that is awful, of course, but the real "horror story" elements of Berkowitz's case are as follows. Back in the '90s, Berkowitz changed his confession to add that he'd been part of a Satanic cult and was shooting people to carry out ritualistic murders. But here's the real kicker: He blamed his actions on his neighbor Sam Carr's dog, a labrador retriever named Harvey, which he told the authorities was possessed by an ancient demon that ordered Berkowitz to kill people.
Now try watching FX's Wilfred without thinking about that every second.