Lex Van Lieshout / EPA Books about the anniversary of the assassination of US president John F. Kennedy are on display in a store window in The Hague, The Netherlands, Friday.

The Warren Commission report -- the 888-page document produced by the committee appointed by President Lyndon B. Johnson to investigate John F. Kennedy’s assassination -- remains the official account of what happened in Dallas on Nov. 22, 1963.

But in the decades since, the report, which determined that Lee Harvey Oswald acted alone, has created more uncertainty than closure, according to a new book by former New York Times investigative reporter Philip Shenon.

“At the end of the day, unfortunately, the Warren Commission left so many questions unanswered that we will probably forever more have to deal with conspiracy theories about the assassination,” said Shenon, the author of A Cruel and Shocking Act: The Secret History of the Kennedy Assassination.

As the 50th anniversary of Kennedy’s death approaches, a majority of Americans – 59 percent – believe in some sort of conspiracy behind the assassination, according to a poll by the Associated Press and GfK, a public opinion research firm.

The poll, conducted in April, found that nearly one in six Americans suspect that multiple people were involved in a plot to kill the president. Twenty-four percent believe Lee Harvey Oswald acted alone and 16 percent are unsure. A Gallup poll from 2003 found that three-quarters of Americans subscribe to some sort of conspiracy theory, though there was no consensus – mafia, Cuban or Soviet involvement, perhaps? – about which theory to believe.

Shenon blames four Washington men for spawning “conspiracy theories that are likely to plague us forever.” They are: former CIA Director Richard Helms, former FBI Director J. Edgar Hoover, former Supreme Court Chief Justice Earl Warren and Robert F. Kennedy, for publicly supporting the Warren Commission despite denouncing it privately.

Shenon, who spent five years researching his book, said his reporting uncovered that both the CIA and FBI had Oswald under surveillance for an extended period of time prior to Kennedy’s murder.

“The question becomes, 'Why didn’t they act on that information?'” Shenon said.

Yet Shenon’s book is most concerned with the destruction of evidence by U.S. officials, who after the assassination destroyed items including: a letter Oswald left for the FBI, Kennedy’s original autopsy report, and photographs of a trip Oswald took to Mexico, where Shenon said he met with Cuban and Russian spies. Shenon suggests that because of the FBI and CIA’s decision to ignore Oswald in Dallas, the agencies were forced to cover up their mistakes.

“The interactions between Oswald and these people were completely uninvestigated by the CIA and FBI,” Shenon said. “They really didn’t want to get to the bottom of it. And I think they didn’t want to get to the bottom of it because they didn’t want to reveal just how much they had really known about Oswald before the assassination.”

And with no trial for Oswald, who was killed by Dallas club owner Jack Ruby two days after the assassination, there was never an opportunity to publicly display of the evidence, which may have settled all the conspiracy talk decades ago.

Another obstacle? Oliver Stone’s 1991 thriller JFK, which has been criticized for taking liberties with historical facts and promoting various conspiracy theories (including that LBJ was part of an assassination plot), was a major commercial success, grossing upward of $205 million at the box office.

Or maybe, like Stone's film, the conspiracy theories generally just make for good drama.

“It’s a detective story and people love detective stories,” Shenon said. “It’s the ultimate homicide case.”

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