''This is the Zodiac speaking. I like killing people because it is so much fun...the most thrilling experience...'' This shocking true crime classic is now a major movie. A sexual sadist, the Zodiac's pleasure was torture and murder. He taunted the authorities with mocking notes telling where he would strike next. The official tally of his victims was six. He claimed 37 dead. He was never caught. Author Robert Graysmith tells the inside story of the hunt for the hooded killer, and finally reveals his possible true identity. The new movie ''Zodiac'' is based on this book. Directed by David Fincher (''Fight Club''), it stars Jake Gyllenhaal as Graysmith himself, Robert Downey Jr and Chloe Sevigny.