His interest in UFOs grew out of the incidents involving pilots Kenneth Arnold in 1947 and Thomas Mantell in 1948. His flying saucer career really began in 1953 when he drove across the country "tracking the elusive flying saucer" in preparation for his planned book. He interviewed almost 100 UFO experts and eyewitnesses: he visited the Pentagon and examined their files on UFO investigations; he visited the Project Blue Book facilities at Wright-Patterson Air Force Base in Dayton, Ohio, meeting Col. Bob Friend; he interviewed the famous saucer author Major Donald E. Keyhoe, and felt that "Keyhoe routinely made too much out of too little, at least in part just to sell books"; he went to Mt. Palomar, California, where "Professor Adamski was holding court" in his hamburger stand; he met Gray Barker, who was to become his long-time friend and collaborator; he interviewed best-selling author Frank Scully; he attended the "Giant Rock" contactee convention and interviewed many witnesses, researchers and officials. He even met former President Harry S. Truman at his office in Independence, Missouri, and asked him about flying saucers. In what became one of Moseley's favorite anecdotes, Truman responded jokingly, "I’ve never seen a purple cow, I never hope to see one."