WAS Marilyn Monroe murdered? Richard Belzer thinks so. Having played Police Det. Munch on “Law & Order” for many years, Belzer has become a detective in real life. Plus, he’s the author of “UFOs, JFK & Elvis: Conspiracies You Don’t Have to Be Crazy to Believe.” Belzer recently filmed an interview at the Friars Club with Keya Morgan for Morgan’s documentary, “Marilyn Monroe: Murder on Fifth Helena Drive.” Morgan, who spent 10 years investigating the screen legend’s death, told Page Six: “I know for a fact that she was murdered.” Belzer said, “It was very fishy.”