Marx is a screenwriter and author. His first film was "Snap, " directed by Chuck Vincent in 1981 (Lone Star Films) starring Chris Lemmon. He wrote many films for Cannon in the 1980s. He recently co-authored Joe Franklin's autobiography, "Up Late with Joe Franklin" (Scribner, 1995). He has written extensively on crime and terrorism, covering the Oklahoma City bombing and publishing "America Under Attack" (Carlyle Communications, 1995).