It was 12.30pm on November 22, 1963, as John F. Kennedy greeted the crowds of Dallas from his ceremonial motorcade, when the shots rang out over Dealey Plaza that killed the president and ended the "Camelot" era.

Within hours, a gunman's nest was discovered in the nearby Texas Schoolbook Depository, and one of its employees, Lee Harvey Oswald , was arrested. Two days later, he in turn was shot and killed in a police station by nightclub owner Jack Ruby , who said he wanted to spare Kennedy's wife Jackie from having to testify at Oswald's trial. The Warren Commission , which investigated the assassination, concluded that Oswald had acted alone, but conspiracy theories have flourished ever since. Most accept that Oswald (an ex-Marine who defected to Russia and returned with a Russian wife) fired the shots, but see him as the fall guy in a larger plot, variously attributed to the Mafia, anti-Castroists, Cuba, the KGB and US government agencies. Claims by witnesses to have heard shots on the famous Grassy Knoll on the north side of Elm Street remain unsubstantiated, but visitors can usually be found sniffing around here for clues - along with self-styled guides, ready to engage them in costly conversation. Senate inquiries were finally closed down by the Justice Department in 1988, arguing that there was no "persuasive evidence" of any plot.