Fort Worth, Texas ? Forty years after his death, nowhere is the memory of John F. Kennedy more alive than in the ongoing drama over who killed him and why.

Only 32 percent of American adults accept the finding that Lee Harvey Oswald acted alone, according to an ABC News poll. The poll, conducted earlier this month, found that 70 percent think the assassination was part of a broader plot; 51 percent believe there was a second gunman; and more than two-thirds believe there was a government cover-up. It is the stuff of countless books and speeches.

“I’m going to give a talk to about 1,000 students who could not be more interested in what went on,” Kermit Hall, Utah State University president, said recently. “What interests them is, they want to know how the conspiracy worked.”

But whose conspiracy was it — the mob, the Cubans or even members of Kennedy’s own government? Believers have suggested everyone from Lyndon Johnson and former FBI chief J. Edgar Hoover to agents of the Soviet Union’s KGB intelligence service.

There’s no consensus among theorists on how a conspiracy worked, but Hall, who served in the 1990s on the congressionally mandated JFK Assassination Records Review Board, is sure of one thing: Kennedy assassination conspiracy theories continue to proliferate because officials have kept too much of the assassination data under wraps.

Another academic expert said the persistence of assassination conspiracy theories is simply part of a longstanding American tradition.

“People will believe forever, no matter the reliability of the evidence,” said Charles Stewart, a Purdue University communications professor who studies and teaches how conspiracy theorists make their conspiracies believable. “We love conspiracies in this country. Even back to the colonists, Americans always have been suspicious about their government and have rallied around conspiracies.”

Some experts have suggested that the Vietnam War and Watergate deepened Americans’ cynicism and eroded trust in government.

“Many people look at the Kennedy assassination as a turning point, when people started realizing and thinking and believing their government would lie to them and lie to them repeatedly,” said Gary Mack, curator of the Sixth Floor Museum at Dealey Plaza in Dallas.

But after poring over thousands documents, photos and other assassination materials with the review board, Hall has decided that the distrust all goes back to secrecy.

“The opportunity for full disclosure didn’t occur because the evidentiary base was for years kept from the public,” Hall said. “The result was, in an evidentiary vacuum, the idea of conspiracy was allowed to grow almost unabated.”

Creating a high-level panel such as the Warren Commission, then failing to turn over all the information, only fed the conspiracy mill, Hall said. The Warren Commission’s conclusion was that Lee Harvey Oswald acted alone.

“One could easily understand that the Warren Commission could get it right and wrong, simultaneously,” said Hall, who with his fellow review board members issued a final report in 1998.

Perhaps the most persistently questioned finding of the Warren Commission is the “magic bullet” theory.

The theory assumes that Oswald alone fired three shots and that one bullet zigzagged through both Kennedy and Texas Gov. John Connally. The bullet is said to have gone through Kennedy’s throat, then into Connally, puncturing his lung, hitting his rib and wrist and then exiting relatively unscathed.

Some historians, forensic experts and conspiracy theorists do not buy it.

James Fetzer, author of “Assassination Science: Experts Speak Out on the Death of JFK,” says the Kennedy X-rays and the film of the assassination by bystander Abraham Zapruder were fabricated and that there were actually six or so people firing at the president that day.

“The driver actually brought the limo to a halt to make sure Kennedy was hit enough times to be killed. The Secret Service set him up, and we have more than 15 indications of them doing that,” Fetzer said. “The order of vehicles in the motorcade were wrong, that’s perhaps the most telling. Nixon knew about it, too. J. Edgar Hoover and LBJ were involved as well, I’m sorry to say.”

In 1967, New Orleans Dist. Atty. Jim Garrison asserted that the assassination was a CIA-led coup. Garrison’s theories went to court — and eventually to Hollywood as Oliver Stone’s 1991 movie “JFK” — but Clay Shaw, the alleged “evil genius” behind the assassination, was acquitted in less than an hour.

Technology has only solidified positions.

Conspiracy theorists now use the Internet to bounce their ideas around the globe, build databases and convert a new generation of believers.

ABC and Court TV both ran sophisticated computer simulations this month of the crime scene and an analysis of a police audiotape, asserting that the Warren Commission got it right — Oswald alone killed Kennedy.

The now-digitized Zapruder film shows exact moments — such as the second when Connally’s lapel flew up — that indicate precisely when he was shot and his position relative to the president. Their conclusion: Connally, who sat in front of Kennedy, was turning when he was shot, making the bullet’s path plausible.

Many Americans nevertheless find it difficult to believe that a nobody like Oswald — a former Marine who went to live in Russia, became disenchanted with life under communism, and took a dead-end job in Texas — could have single-handedly killed the leader of the free world.

Some 6 million documents have been released by the Assassination Records Review Board, but Hall said he doubted any revelations would come from them.

“The lesson of American history is, by and large, unhappy small-time people, if you will, make more of their life by shooting or killing better-known people,” Hall said.