In '' Behold a Pale Horse '' , Cooper asserted that President John F. Kennedy was assassinated because he was about to reveal that extraterrestrials were in the process of taking over the Earth . According to a " top secret " video of the assassination that Cooper claimed to have discovered , the driver of the presidential limousine , William Greer , used " a gas pressure device developed by aliens from the Trilateral Commission " to shoot the president from the driver 's seat . The Zapruder film shows Greer twice turning to look into the back seat of the car ; Cooper theorized that Greer first turned to assess Kennedy 's status after the external attack , and then to fire the fatal shot . Conspiracy theories implicating Greer reportedly " snowballed " after publication of '' Behold a Pale Horse '' . Cooper 's video purporting to prove his theory was analyzed by several television stations , according to one source , and was found to be " ... a poor-quality fake using chunks of the ... Zapruder film . " As Cooper moved away from the Ufology community and toward the militia and anti-government subculture in the late 1990s , he became convinced that he was being personally targeted by President Bill Clinton and the Internal Revenue Service . In July 1998 he was charged with tax evasion ; an arrest warrant was issued , but Cooper eluded repeated attempts to serve it . In 2000 , he was named a " major fugitive " by the United States Marshals Service
assassinated
Assassination of John F. Kennedy
Milton William Cooper