William F Buckley was "Umbrella Man" who signaled the shooters on the Grassy Knoll all systems were go when US President John Kennedy was shot from ambush in Dallas, TX. Nov. 22, 1963, his accomplice was Corsican adventurer Lucien Sarti .. after the assassination Buckley and his CIA classmate E Howard Hunt went to Mexico and are thought to have engineered the 1968 Tlatelolco Massacre that had a death toll of thousands. The Assassination of John F Kennedy.