Doubts that just won’t die

It can take a few minutes to spot them: a pair of white Xs on the ground along Dealey Plaza, signifying where President John F Kennedy was shot. Stay long enough at this Dallas intersection and you'll see tourists scurrying out between traffic, squinting up at a certain point in the distance, gauging the same calculation in their head.

It's 264ft from here to the window from which lone gunman Lee Harvey Oswald shot Kennedy, firing three shots at his passing motorcade from the sixth floor of the Texas School Book Depository. Eighty per cent of people in the US believe he didn't act alone. His motive has never been clearly established because within 48 hours of the shooting, Oswald – a communist sympathiser claiming to be set up – was gunned down in custody by Jack Ruby, a nightclub owner with ties to organised crime.

Fifty years on, the same questions linger. Despite the 3,000 pieces of evidence collected and the 32 people who photographed or filmed the assassination, the appetite for answers is insatiable. The book depository has become the Sixth Floor Museum: a comprehensive illustration of Kennedy’s assassination. Its centrepiece is the corner Oswald allegedly used as a sniper’s perch, hidden behind a barricade of boxes, recreated to appear as it did on November 22, 1963.

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The presidential limousine is followed by secret servicemen on running boards. Photograph: AP

"We're still not sure what happened that day," says museum worker Ken Crump. "We let people decide for themselves."

The need for answers has lured doubters to Dealey Plaza since long before the museum opened. Take away the vendors selling postcards, and the setting remains largely unchanged since 1963. There’s the grassy knoll adjacent to Elm Street, where 56 witnesses located gunfire, and the picket fence behind it, where interpretations of acoustic evidence placed a shooter.

You can also stand on the concrete pedestal from where bystander Abraham Zapruder filmed the crucial footage of Kennedy's head being thrown to the rear and left – a point many have relied upon as evidence of a bullet coming from somewhere other than the book depository.

Phantoms and anomalies
But what fixates conspiracy theorists are the things that disappeared without a trace. Pursuing the phantoms and anomalies captured in grainy footage has become a subculture. Facts are met with counter-facts, spawning one subsidiary argument after another. Even official investigations have conflicted. The Warren Commission's report, published in 1964, concluded that Oswald acted alone. In 1978, the US House Select Committee on Assassinations found the assassination was "probably" a conspiracy, though by whom it wouldn't say.

Shoddy evidence, marred by complacency and concealment, has hampered inquiries. Despite a large police presence, Dealey Plaza was not properly searched or secured following the shooting. Two-thirds of witnesses were never interviewed and most just walked away. One of the three bullets Oswald fired was never accounted for, while a fragment of Kennedy’s skull found along the highway was handed in the next day, its exact location unclear. The crime scene was poorly managed: spent rifle casings were collected by bare hands and removed before police photos could be taken.

At Parkland Hospital, the handling of Kennedy's body flouted standard procedures. No drawings of entry or exit wounds were made. Contravening Texan law, Secret Service agents removed Kennedy's body before an autopsy could be performed, leading to a scuffle when hospital staff objected. Kennedy was then taken to Bethesda Naval Hospital in Maryland and every part of what followed – right down to a changing of caskets – has been scrutinised for signs of interference.

Official reviews of the autopsy found it to be incomplete and inaccurate, though consistent with the finding that Kennedy was struck by two rifle shots from behind. There are significant disparities, however, between the autopsy photos and the damage observed by witnesses at both hospitals. Several claimed that the back of Kennedy’s head was blown out, believing it to be the result of gunfire from the front.

Sandra Spencer, who processed the autopsy film, later claimed that the official photographs held in the National Archives were unrecognisable from the ones she developed and were even printed on different paper. Individually, these lapses may be insignificant. Combined, they're the perfect source material for conspiracy theorists.

Within a week of the assassination, President Lyndon B Johnson established the Warren Commission, which some saw as a politically motivated attempt to quell public unease before the 1964 presidential elections, which Johnson won. Others believed that implicating the Soviets or Cubans would have risked nuclear war, thereby necessitating a cover-up.

'Single bullet'
After 10 months, the commission concluded that Oswald was the lone shooter. Central to this was the 'single-bullet' theory, which claimed that one bullet ripped through Kennedy's upper back and throat before striking Texas governor Connally (who was sitting in front of him) through his ribs, wrist and thigh. But the bullet had been recovered intact, on a stretcher in Parkland Hospital without any trace of blood or tissue. The bullet matched Oswald's rifle, however, so subsequent studies have deemed the trajectory plausible.

In 1976, the House Select Committee on Assassinations was formed after reported abuses among US intelligence agencies helped foster an atmosphere of distrust. Following Watergate and Vietnam, there was growing belief that US foreign policy had led the country in a different direction since Kennedy's death and that the same agencies responsible for evidence in the assassination had also been conspiring to assassinate other world leaders.

The committee’s investigation was swayed by a recording from the radio of a police motorcycle officer that established a second gunman firing the third of four shots from the grassy knoll – a conclusion that has been repeatedly contested.

But even if a conspiracy could be ascertained, there is no consensus on who was responsible. Potential suspects: the CIA, the KGB, the mafia, then-vice president Johnson, the FBI, the Secret Service, various right-wing extremists as well as both pro- and anti-Castro Cubans.

Some even argue that the real target may have been Governor Connally, who rejected Oswald's petition to reverse his dishonourable discharge from the Marines; others cite Oswald's visit to the Cuban and Soviet consulates in Mexico seven weeks before the assassination as significant.

Ruby’s murder of Oswald has generated more theories. Not only was he able to gain access to Oswald, but he was spotted at the Dallas Police Headquarters several times after Oswald’s arrest. In 1965, Ruby claimed to be a pawn for figures in power and that the truth would never surface – a claim he recanted on his deathbed two years later.

Any number of compelling narratives can be squeezed from the contradictions, connections and conundrums that define the JFK assassination. Perhaps the appeal is is that conspiracy theories offer a way of plucking meaning from disorder. Or perhaps the simple explanation – that a lone misfit changed history – just seems unsatisfactory by comparison.