Kennedy conspiracy theories in overdrive as 50th anniversary approaches, with John Kerry the latest to voice his suspicions

Who killed JFK? Fifty years on, slew of new books add fuel to conspiracy fire

When John Kerry fuels doubts that Lee Harvey Oswald acted alone just as publishers unleash a torrent of JFK assassination books you have to ask yourself: conspiracy?

Did the the secretary of state pull the trigger on a clandestine publishing industry marketing plan? Are bookstores in on it? Is Hollywood connected? Or did Kerry act alone? We may never know.

We do know that Kennedy nostalgia and scrutiny are in overdrive on the eve of the 50th anniversary of his murder, with dozens of new books advancing theories novel and dusty over who fired the fatal shots at the motorcade in Dallas.

Options include Fidel Castro, the mafia, the CIA, J Edgar Hoover, Lyndon Johnson, the secret service or, on the far outer fringes of speculation, Joe DiMaggio.

Kerry caused astonishment when he waded into the debate by telling NBC that he suspected Oswald had external help or inspiration, possibly from Cuba or Russia. "To this day, I have serious doubts that Lee Harvey Oswald acted alone."

The comments added unexpected spice to the latest revelations and claims of revelations about the most parsed, analysed and disputed moment in US history.

John and Jackie Kennedy smile at the crowds lining the motorcade route in Dallas, Texas, on 22 November 1963. Photograph: Bettmann/Corbis

Major US publishing houses have produced dozens of titles pegged to the November 22 anniversary, swelling a bulging oeuvre of more than a thousand Kennedy-related books dating back half a century.

The independent house Skyhorse Publishing alone is publishing 25 assassination-related titles this year, including Blood, Money & Power: How LBJ Killed JFK, by Barr McClellan, and Destiny Betrayed: JFK, Cuba and the Garrison Case, by James DiEugenio.

"Every publisher wants to have a book out," said Jim Milliot, co-editorial director at Publishers Weekly, the industry bible. "Baby boomers are big book buyers and JFK was the baby boomers' president."

Fascination will wane as Kennedy becomes more a historical than mythical figure, he predicted, but for now publishers were mining every conceivable angle. "There are so many out there, consumers have a lot to choose from. Maybe that's why none in particular has jumped to the top of the bestsellers."

Polls tend to show that most Americans reject the Warren commission's finding that Oswald, acting alone, fired all three shots from the Texas book depository's sixth floor.

That's a view long shared by senior government officials, said Jeff Morley, an author and former Washington Post reporter who moderates the site JFK Facts. "John Kerry is part of a long tradition of insiders who have questioned the official version."

Morley's 2011 book, Our Man in Mexico: Winston Scott and the Hidden History of the CIA, plumbed the agency's dealings with Oswald before the assassination. He thinks it implausible that "one guy with no motive" singlehandedly did it but says truth remains elusive. "Chunks of the story we don't know."

Morley accused major organisations of being "asleep at the wheel" in neglecting available documentation and not demanding access to still-sealed archives. Another problem was that ludicrous and discredited theories competed for attention alongside serious investigations. "The bad information obscures debate."

One version posits that DiMaggio (a duck hunter in his spare time) was seeking revenge for JFK allegedly romancing his ex-wife Marilyn Monroe.

Another says a man with a black umbrella filmed along the route fired a poison dart. Another points the finger at a secret service agent whose regicide was edited out of the Zapruder footage. To guide readers through the conspiracy maze here is a list of five new books, each representing, with varying credibility, a popular theory.

Lee Harvey Oswald and Jack Ruby. Was Oswald the lone gunman? Photograph: Bob Jackson/AP

1. The mob did it

• The Hidden History of the JFK Assassination, by Lamar Waldron (Counterpoint)

Thesis: Godfathers Carlos Marcello and Santo Trafficante took out the president to neutralise his anti-mafia crusade. They framed Oswald and his supposed Cuban puppet-masters, a ruse which deceived LBJ and, to this day, Kerry.

"They got away with it because they planted the evidence against Castro," said Waldron. A cover-up endures. "We know the FBI had Marcello's confession in 1985 and basically suppressed it."

A Warner Brothers film due out next year, based on this and a previous book co-authored by Waldron, will star Leonardo DiCaprio and Robert De Niro. "We hope the movie will bring attention to the fact hundreds of (government) files haven't been released."

2. The CIA did it

• CIA Rogues and the Killing of the Kennedys: How and Why US Agents Conspired to Assassinate JFK and RFK, by Patrick Nolan (Skyhorse)

Thesis: Top spooks Richard Helms and James Jesus Angleto hired mafia hitmen to murder Kennedy to derail his planned disengagement from Vietnam and rapprochement with Cuba and the Soviet Union. "Their motive was power, self-preservation."

Nolan cites research by "world-famous forensic scientist Dr Henry Lee", who writes the book's foreword, to argue there was more than one gunman. Nolan's website says he "utilizes the mosaic method of intelligence, analyzing each piece that is obtained and determining its relationship to other pieces to arrive at the solution".

LBJ sworn in aboard Air Force One. Photograph: Cecil Stoughton/Bettmann/Corbis

3. Lyndon Johnson did it

• The Man Who Killed Kennedy: The case against LBJ, by Roger Stone (Skyhorse)

Thesis: The vice-president orchestrated an elaborate plot involving elements in the mob, CIA, White House and Cuban exile community to eliminate his boss. The motive: JFK planned to dump LBJ from the ticket in 1964, leaving him exposed to corruption probes.

The Texan Johnson's control over Dallas police facilitated the cover-up of evidence such as a fingerprint in the book depository's sniper's nest which matched his personal hitman, Mac Wallace.

The truth, says Stone's Amazon entry, was hiding in plain sight all this time. "LBJ was not just shooting his way into the White House, he was avoiding political ruin and prosecution and jail for corruption at the hands of the Kennedy's (sic)."

4. Oswald did it with Cuban help, or inspiration

• A Cruel and Shocking Act: The Secret History of the Kennedy Assassination, by Philip Shenon (Henry Holt and Co)

The thesis: Oswald flirted with Cuban officials in Mexico City shortly before the assassination and possibly had help setting it up. At the very least, he hoped to impress the Castro government. The CIA, FBI and others in Washington sabotaged the Warren commission by withholding evidence to protect reputations and cover up their own missteps in dealing with Oswald before the murder. Reviewers have praised the former New York Times investigative reporter's tome as a sober, balanced account.

5. Oswald acted alone

• History Will Prove Us Right: Inside the Warren Commission Report on the Assassination of John F Kennedy, by Howard Willens, (Overlook)

The thesis: A loner with a rifle and a grudge did it alone.

Willens, one of the commission's few living staff members, gives a behind-the-scenes take on the investigation, its personalities and methodology. One by one he discards alternatives to the lone gunman theory.

Willens admits mistakes in the investigation, but says these did not affect the veracity of its ultimate conclusion. He defends chief justice Earl Warren's prediction that "history will prove that we are right".

For sceptics this is the greatest conspiracy theory of all, a brazen lie to whitewash the crime and aftermath.