Helter Skelter by Vincent Bugliosi & Curt Gentry - the scariest book I've ever read. Most likely because it is true; it discusses what really went on during the Manson Murders. If you have the guts, read it.
Charles Manson is a convicted serial killer who has become an icon of evil. In the late Manson founded a hippie cult group known as "the Family" whom he manipulated into brutally killing others on his behalf.