For years, Americans have viewed President John F. Kennedy's assassination through conspiracy-colored glasses. Writers, filmmakers and Web-site authors have blamed his death on a sinister network of shady operators: Cuba's Castro, the Mafia, the CIA -- even Lyndon Johnson. But two experts say new research shows Kennedy was killed by two bullets fired by a lone gunman, Lee Harvey Oswald. Relying on chemical, ballistic and statistical analyses, they say their work dispels more than 100 conspiracy theories tied to Kennedy's death. "It's preposterous on the face of it to believe that a mousy little guy with a $12.95 rifle could bring down the leader of the free world," said Kenneth A. Rahn, a retired University of Rhode Island atmospheric chemist. "Yet, that's exactly what Lee Harvey Oswald did 41 years ago." Rahn, who lives in Narragansett, R.I., and ballistics expert Larry M. Sturdivan, who lives in Santa Fe, N.M., published their findings in two articles in last month's Journal of Radioanalytical and Nuclear Chemistry. Kennedy, 46, was fatally shot on Nov. 22, 1963, as he rode in a motorcade through Dallas. A year after his death, the Warren Commission concluded that Oswald was the sole assassin. Conspiracy theorists, however, continue to advance alternative plots involving other shooters and planted evidence. Gallup polls show that roughly three out of four Americans believe the conspiracy theorists. According to Rahn and Sturdivan, the FBI used old chemical technology to analyze five bullet fragments recovered after the shooting. Later, they placed the fragments in a nuclear reactor to analyze their chemical properties. "But the FBI was new to this technique. At the end of the day, they didn't know what to make of it," so J. Edgar Hoover, the FBI's director, "kept it a secret," Rahn says.