Key Witness Metro-Goldwyn-Mayer  1963 Presents an Avon Picture produced by Kathryn Hereford Directed by:  Phil Karlson Based on the novel by Frank Kane Starring:  Jeffrey Hunter, Pat Crowley, Joby Baker, Susan Harrison, Johnny Nash, Dennis Hopper Dennis Hopper plays the role of Cowboy, leader of a gang of switch blade wielding dope addicts and sex fiends. One gang member is named Muggles an old slang term for marijuana cigarettes.