For Americans, JFK will never be case closed

Half a century on, it remains the defining collective trauma of the baby-boom generation: the "Where were you…?" moment when you heard that a young American president, in whom so much hope was invested, had been assassinated in Dallas. But a second question persists today, if anything even more stubbornly. Did Lee Harvey Oswald really do it all on his own?

As the 50th anniversary of 22 November 1963 draws closer, the cottage industry of Kennedy conspiracy theorising has become a mighty factory conveyor-belt. For weeks now conferences, lectures and seminars have been taking place across the United States and beyond. In just three months 100 books have been added to the 1,500 or so that already form the Kennedy canon, not to mention the dozens of websites on the subject.

And that the raw material exists cannot be denied – even by those like this writer who are firm believers in the cock-up rather than conspiracy theory of history, and who have trouble understanding why Americans, generally down-to-earth and "just the facts ma'am" in their approach to life's enigmas, seem to be suckers for the latter.

Suggestions of a cover-up began well before the commission to investigate the assassination, headed by Chief Justice Earl Warren, delivered its 888-page report 11 months later. Rival schools quickly coalesced: a smaller one accepting the report's conclusion that Oswald acted purely on his own initiative, as did Jack Ruby when he shot Oswald at Dallas police headquarters on 24 November, 1963; and a much larger one convinced that Oswald was a pawn in a bigger plot. The former believed that the conspiracists were paranoid obsessives, the latter that anyone who agreed with the report was naive or worse.

The commission's report was certainly not perfect; evidence emerged later that would cast doubt on some its findings. But every subsequent official inquiry has produced the same basic finding, that Oswald acted alone. Nothing though would convince those who could not accept that a petty sociopath, on his own, could have been responsible for a deed of such colossal consequence.

In the years since, beyond the incontrovertible facts that both Kennedy and Oswald were killed, no aspect of the case has been left unchallenged: the number of shots fired, from where and by whom; the autopsy; the film and audio tapes of the assassination; whether evidence was suppressed or falsified; whether witnesses had been systematically eliminated. Indeed 50 years of twists and turns in the conspiracy arguments merit their own separate history.

The first book alleging conspiracy – Thomas Buchanan's Who Killed Kennedy? – appeared in May 1964. Two years later, the lawyer Mark Lane published Rush To Judgment, a best-selling, and highly influential critique of the Warren findings. In 1979, the House Select Committee on Assassinations (HSCA) agreed with Warren that Oswald had fired the shots, but that a conspiracy was "probable", in which a second gunman was involved.

By 1991, the number of published works proposing conspiracies was already counted in dozens. Then Oliver Stone's thriller JFK hit the screens, re-igniting the controversy even though many critics panned the movie as a travesty of the facts. Then the investigative journalist Gerald Posner countered with Case Closed in 1993, that backed Warren's findings. No single volume so infuriates the conspiracy theorists, but none has made the "debunkers" case so powerfully. A final twist came in 2003, with Blood, Money & Power: How LBJ Killed JFK, by the Texas lawyer and businessman Barr McClellan. Quickly discredited, the book gained delicious extra notoriety because the author's son, Scott, happened at the time to be the White House press secretary, for George W Bush.

So who is alleged to have been behind the murder? The shifting cast of suspects is vast, from the Soviet Union and Fidel Castro to anti-Castro Cuban exiles, from government agencies like the CIA and FBI to the Mafia and organised crime, from the US military/industrial complex to individuals who may have hated Kennedy, from FBI director J Edgar Hoover to vice-president Lyndon Johnson.

The early frontrunners were the Soviet Union and Fidel Castro's Cuba; the first not only because Oswald had once defected there, but also on the theory that the Kremlin was thirsting to avenge its humiliation in the Cuban missile crisis. As for Castro, he was repaying in kind the CIA's attempts to kill him. But neither made sense. Unmasking the crime would have unleashed terrible, even thermo-nuclear, revenge from Washington.

The focus then switched to clandestine US agencies. The CIA, it was said, was enraged by Kennedy's pulling of the plug on the botched Bay of Pigs invasion of 1961, and fearful it might be stripped of its para-military operations. As for the FBI, did not its legendary director Hoover detest the youthful president and the interference of his pushy brother Robert, then US attorney-general?

More recently, the emphasis has swung back to Cuba, to anti-Castro Cuban exiles convinced that JFK had betrayed them over the Bay of Pigs. Increasingly, it was suggested they were acting in concert with the Mafia, incensed by Bobby Kennedy's crackdown on organised crime, and anxious to regain its lucrative pre-revolution gambling business in Cuba.

Some all along stuck to Stone's JFK theory, that powerful domestic defence interests, alarmed that Kennedy would pull out of Vietnam and thus cost them lucrative future business, were behind the plot. In this endeavour, they were supported by Johnson. Indeed, by the crude logic of cui bono? (who stands to gain?) LBJ is right up there. His relations with Kennedy were never good, there were reports he would be dropped from the ticket in 1964; but if Kennedy was eliminated beforehand, who would inherit the Oval Office?

But before we go further, a couple of other near-unassailable facts. First, almost no one disputes that Oswald fired three shots from the sixth floor of the Texas School Book Depository; second, there is no physical trace at Dealey Plaza of another bullet or gun being used that day. The Kennedy Half Century, a new book by Larry Sabato, political professor at the University of Virginia, effectively demolishes evidence of a fourth bullet fired from the whereabouts of the "grassy knoll", to the right of the Kennedy motorcade, central to many conspiracy scenarios and which so impressed the HSCA in 1979.

The key therefore is to prove Oswald was directly linked to a specific, broader conspiracy. "You must tie in Lee Harvey Oswald, a person that I'm convinced is the only shooter at Dealey Plaza, to the conspirators," says Gerald Posner. "That's where every conspiracy fails." Those words were spoken in an interview in November 2003, the 40th anniversary. And despite the coincidences and connections which ensure the Kennedy case will never go away, nothing has really changed.

Jack Ruby had acquaintances in the Mafia, lending weight to claims the mobsters took out Oswald to prevent him talking. Then there was Oswald's stay in the Soviet Union, that would automatically have had the CIA interested (or, again, might he have been a CIA agent all along?). There was Oswald's peculiar summer of 1963 in New Orleans, when he was (or might have been posing as) a pro-Communist Cuba sympathiser.

That sojourn led, by a long and convoluted path, to the only criminal case in the Kennedy assassination that went to court, and upon which the JFK movie was based. It was brought in 1969 by the New Orleans district attorney Jim Garrison against Clay Shaw and charged that the businessman, along with right-wing activists and CIA elements, was involved in a conspiracy in which Oswald was the frontman. The jury acquitted Shaw after a mere hour of deliberation.

Perhaps most persuasive are the CIA's indisputable links with Sam Giancana, Carlos Marcello and Santo Trafficante – the mob bosses who once ran Cuba – spurred by, if nothing else, a shared hostility to Castro. In a memoir, Trafficante's now deceased lawyer Frank Ragano even claimed the dying boss had told him in 1987 that the mob had carried out the hit, but against the wrong Kennedy: "We shouldn't have killed Jack, but Bobby."

Ragano's tale has been discredited, but Tony Summers, one of the most diligent assassination sleuths, has now come up with a variant in Not In Your Lifetime, a new edition of his 1980 book Conspiracy. Summers reveals that an anti-Castro Cuban named Herminio Diaz, who once worked for Trafficante, told a fellow prison inmate that he had fired shots in Dealey Plaza that November day. Diaz however died in 1966. His story reaches Summers at two removes.

And there, roughly, matters now stand. Take a natural human reluctance to believe that so colossal a tragedy could have been brought about by a single individual, and throw in a cacophony of ballistics and experts ready to testify to everything and the opposite of everything – and it's no surprise some 70 per cent of Americans believe that Oswald did not act alone.

That said, it is equally hard to believe that in a system as open as the US's, evidence of a plot would not have emerged by now; some of the cover-ups posited by conspiracy buffs would have required dozens, maybe hundreds, of people in the know. And in 50 years, no one has talked? There is also the immutable law of conspiracy theories – barring discovery of an irrefutable document, contemporary recording, or piece of circumstantial evidence – the further removed from the moment, the less reliable memories tend to be.

This 22 November, in fact, may prove the highwater mark of Kennedy conspiracy theorising. Half a century on, some witnesses and people intimately connected to the tragedy (Oswald's wife and children, for instance, and the daughter of JFK) are still alive, and the Kennedys, with their deeds and misdeeds, still populate the national imagination. But a century on, in 2063, when the baby boomers are long gone? One doubts it.

No one will ever be quite sure why Lee Harvey Oswald chose to murder an American president. But then again, although the strong probability is that Oswald did so entirely alone, no one will ever be quite sure of that either.