Moore wrote The Roswell Incident with Charles Berlitz in 1980, which alleged the 1947 Roswell incident involved a government coverup of an extraterrestrial spaceship crash.
William Moore had a lifelong interest in UFOs, which started during his youth. He became involved in MUFON, the Mutual UFO Network, and left his teaching job to become a full-time freelance writer. In 1980 he co-authored a book on the 1947 Roswell incident with Charles Berlitz. He was also part of a group that helped to circulate documents that alleged of a top secret organization called the Majestic 12, which the documents claimed controlled the U.S. government response to UFOs and ETs phenomenon since 1947.