IT was the crime of the century and changed the course of history. Yet the assassination of U.S President John F Kennedy remains an enigma 50 years later.His death in Dallas is shrouded in conspiracy theories disputing the verdict from 1964's Warren Commission that a lone gunman, Lee Harvey Oswald, was to blame.Debate rages over a magic bullet, Grassy Knoll and the murder of prime suspect Oswald by strip club owner Jack Ruby, two days after JFK's assassination.A House of Representatives Committee on Assassinations declared in 1978 there was a 95 per cent certainty that a second gunman was involved in the President's murder - meaning there was a conspiracy to kill him.And a nationwide poll carried out in May this year revealed 59 per cent of Americans still believe there was a wider plot to assassinate President Kennedy.Those doubts have stained the integrity of the world's most powerful government over the past half a century.Former senior Scotland Yard homicide detective Colin Sutton visited Dealey Plaza with The Sun and tells why he agrees with the conspiracy theorists.While a leading American ballistics expert on the subject explains why he is certain Oswald acted alone.