As a presidential candidate, Jimmy Carter claimed to have seen a UFO. As president, Ronald Reagan mused openly on how petty differences among nations might evaporate in the face of an extraterrestrial threat. And no one has done more to turn up the speculative heat than retired Adm. Bobby Ray Inman, who held a slew of top intelligence posts, including deputy director of the Central Intelligence Agency. In a Learning Channel documentary, Inman said - but has since repeatedly and vigorously denied - that the military is attempting to use technology from unspecified recovered vehicles." The most perplexing UFO mystery of all began in the desert north of Roswell, NM. Ideas of what happened here during the first week of July 1947 range from the simple - a weather balloon crash - to the downright silly - Earth was being scouted for an intergalactic invasion. The latest official government explanation - there have been three thus far - is that the recovered debris came from a Project Mogul balloon that was carrying instruments to detect Soviet nuclear tests. After interviewing witnesses who had seen and handled crash-site debris, and reviewing [classified documents], we have concluded that there really was a crashed disc, dead bodies and a secret that could have been politically deadly to presidents Harry S. Truman and Dwight D. Eisenhower.