Armando Sanchez for TIME "I’m in the business of knowing how so much of what is said here is nonsense,” said John McAdams, a professor of political science at Marquette and student of the JFK assassination.

The air in Pittsburgh was wet, thick, and cold, nothing like the warm, clear conditions on that day in Dallas, the day that changed history, the day that nearly 50 years later had brought all these people here to solve the murder of the President.

“Tonight they can get us all in one drone strike,” Oliver Stone, who directed JFK, told a gathering of Kennedy assassination buffs one evening last month. “This is like going to a meeting of abolitionists in the 1850s. We know we’re all right. But our passion scares them.”

Everyone here at Duquesne University’s International Symposium on the 50th Anniversary of the Assassination of President John F. Kennedy agreed that Kennedy had been murdered, brazenly, brutally. But the old men on the dais and in the audience, with their tweedy getups and rapidly spreading bald spots, could not concur on who had done it and how and why. Maybe Lee Harvey Oswald shot Kennedy. Maybe a second gunman had done it. Maybe he (or they) were acting on Castro’s orders, maybe on Hoover’s, maybe on Johnson’s. A lot of support coalesced around the CIA’s complicity. But who at the CIA would have had the President killed? And how?

Bobbing along like any other tern in this sea of skepticism and paranoia was John McAdams, a 68-year-old associate professor of political science at Marquette. McAdams looked like every anonymous student of the assassination: He, too, had tan pants, a briefcase, and silver hair atop a big head with prominent features. On the last day, before a full house, one speaker praised McAdams for having the guts to turn up. The speaker called for a sarcastic round of applause and then went on with his speech.

“That’s because I’m a debunker,” McAdams said afterward. “I debunk things. I’m in the business of knowing how so much of what is said here is nonsense.”

What an odd business that is for a 1964 graduate of Kennedy High School in Kennedy, Ala., who every so often finds himself attending conventions on Kennedy’s assassination. Though he’s no academic star, McAdams has secured his own kind of prominence by devoting much of his adult life to calling nonsense on the most persistent strain of doubt in U.S. history.

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A few hundred of McAdams’s usual antagonists had traveled to Pittsburgh to hear the likes of Oliver Stone and Cyril Wecht assail the Warren Commission, the blue-ribbon panel Lyndon Johnson charged immediately after the assassination with uncovering the truth. In September 1964, the panel fingered Oswald as the gunman whose bullets, fired from a 6.5mm Carcano rifle perched on the sixth floor of the Texas School Book Depository, had wounded Texas Gov. John Connally and killed Kennedy. No outsider had influenced him; he acted alone. Case closed, as one well-known book would put it later.

But the intervening 49 years had done little to dull skepticism of the report among the broader public: A 2009 CBS News poll said that only 10 percent of Americans believe Oswald acted alone. By the assassination buffs’ accounting, the commission’s research was slipshod or, worse, a deliberate fiction, a murderous and omnipotent cabal’s hoodwinking of the American public by way of incompetent investigators with establishment credentials. They want the case reopened.

At the conference, this battle often played out in third-person plural pronouns. They don’t want the truth to come out. We do. They killed Kennedy. We will solve the crime. “We represent the majority, and we are a hell of a strong majority,” the conference’s founder, Dr. Cyril Wecht, told the audience. “We need to get this case reopened.”

It was easy to get swept up in the spirit of the thing. The assassination seemed sufficiently distant to allow big historical thinking yet recent enough that its shockwaves lingered, and not just among those who remember Camelot fondly. Files Edward Snowden gave to the Washington Post revealed that the CIA requested $14.7 billion in spending for 2013, far more than outside analysts had speculated. Kennedy was famously quoted as telling an official of his administration in 1961 that he wanted “to splinter the CIA into a million pieces and scatter it to the winds.” He feared the ascendant crypto-governmental national-security interests that thrive to this day. And then he was dead. So all of us had to get to the bottom of this.

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As with Kennedy’s war against his own military leaders, McAdams has, since entering this world more than 20 years ago, quarreled with the vast majority of his fellow buffs. He runs one of the most thorough and popular websites on the assassination and manages a busy forum for buffs, the alt.assassination.jfk newsgroup. He matches or exceeds his opponents in intensity. But why? To the Warren Commission doubters, there’s a murder — of the leader of the free world — in need of solving. To McAdams? That’s a little trickier.

He grew up in rural Kennedy — which went for the same-named Democrat in 1960 — and afterward headed to the University of Alabama, during Joe Namath’s heyday. McAdams studied sociology and made “fairly mediocre grades” outside his major. After graduating, he taught high school, and even got a master’s, but he really wanted to teach college students and work with data. So off he went to graduate school for political science (“I applied to Harvard, because that had a nice sound to it”), and then to Marquette, where he’s been since 1981. He published for a while on voter behavior and death-penalty policy, but the journal articles stopped about 15 years ago. He moved on to the JFK assassination, a fringe topic in scholarship but one on which he published a book and still teaches a course. “That’s the nice thing about academia,” he said. “We get to ride our hobbyhorses a bit.”

He’s married with three children. But all have grown and long since left home — he’s a grandfather of three, too — which leaves him with lots of vacant hours. He spends some of them reading about military history and contemporary politics.

But mostly McAdams likes to read and write about the Kennedy assassination, which is to say he likes to brawl. He fights with his fellow buffs on the newsgroups, over email (both in personal conversations and on a private 50-person listserv; the founder, Paul Hoch, says McAdams loves to badger his opponents), in print (JFK Assassination Logic: How to Think about Claims of Conspiracy came out in 2011), in his classroom, and, should the right moment arise at one of these every-so-often confabs, in person. “He’s got that Irish combativeness,” said Max Holland, a contributing editor to The Nation and a fellow Warren Commission defender. And McAdams is indefatigable.

Holland had invited McAdams to come with him to Pittsburgh so that neither lone-gunman man would find himself alone. When McAdams went to his first JFK conference held in Washington in 1995, he went under the assumed identity of Paul Nolan, “manager of a computer store in Sherwood, Wis.,” because he thought he would face too much heat under his own name. He outed himself to the buffs at a luncheon on the last day, and said his disclosure was warmly received.

Yet McAdams’s antagonists have forever seen the story from the D.C. conference as just one sign of the disingenuousness and subterfuge they find in his work. He’s “a self-contained ambulatory propaganda model,” said Jim DiEugenio, the researcher who asked for applause for McAdams at the conference.

“I really don’t trust anything he says,” said Gary Aguilar, a San Francisco ophthalmologist and assassination researcher. (He and McAdams had a nasty battle on the CompuServe message boards in 1995.)

Lisa Pease, a researcher based in Los Angeles, said that McAdams struck her as so tireless, and so illogical, that someone must be paying him to make his case. Naturally, she looks at his by-the-book conservative views, proclaimed disinterest, and his ties to government-funded research organizations, and thinks, well, CIA. For the record, McAdams says he has never been in the CIA — “Those people think the CIA cares a lot about them. It does not!” — and that he’s just an even-keeled hobbyist who processes the facts and reaches the most natural conclusion, which, at this point, is that Oswald killed the President.

Stan Wayman / Time & Life Pictures / Getty Images John F. Kennedy’s flag-draped casket lies in state in Washington, D.C., November 1963. More LIFE photos from the funeral

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Every momentous event in American history comes with its own corresponding conspiracy theory. They faked the moon landing. Edwin M. Stanton, Abraham Lincoln’s secretary of war, put John Wilkes Booth up to it. Barack Obama was cloned from the DNA of an Egyptian pharaoh, or born in Kenya. Or both!

As rich as the American tradition of conspiracy theories is the sociological tradition of trying to understand why people believe them. Richard Hofstadter’s The Paranoid Style in American Politics is the genre’s ne plus ultra. Hofstadter, writing in 1964, identifies right-wingers driven by rage as responsible for most of the era’s otherwise inexplicable political movements (McCarthyism and the John Birch Society). Any observer of American culture can follow this thread through to the present-day acolytes of conspiracy-geysers Glenn Beck and Alex Jones.

But the Warren Report skeptics fit another mold. They’re sorrowful, not angry. “If only Kennedy had lived,” begin so many of their idle thoughts. Kennedy would never have escalated the war in Vietnam; he would never have let 60,000 American soldiers and countless civilians die in Southeast Asia. They believe he would have defused Cold War tensions and shrunken the American nuclear arsenal. They believe he really would have scattered the CIA to the winds.

You will find precisely none of that in the Warren Report, which builds its case instead with an inquiry into forensics and Oswald’s background, like any other criminal investigation. It’s horribly unthinkable, what the commission contends — that a confused, strange man with a mail-order rifle could, acting on his own, reorient American history. Surely the universe contains more order and meaning.

The whole business of doubting the Warren Commission began before there even was a Warren Commission, with one memorandum passed between White House staffers on the day of Kennedy’s interment at Arlington. Nicholas Katzenbach, who was functioning as Johnson’s attorney general, wrote White House special assistant Bill Moyers, “The public must be satisfied that Oswald was the assassin; that he had no confederates who are still at large; and that evidence was such that he would have been convicted at trial.” Johnson empaneled the Warren Commission four days later.

The memo did not surface until 1978, but perhaps the delay suited the skeptics even better: Those who already believed that someone had covered up a conspiracy now had evidence that the highest powers in government had considered the benefits of something that looked a great deal like a cover-up. And they had done so less than 24 hours after the blast from Jack Ruby’s .38 Colt Cobra had killed Oswald. Oswald had told police he was “just a patsy.”

Add a House committee report, which concluded Kennedy had “probably been assassinated as result of a conspiracy,” and the Zapruder film — which was in 1975 broadcast on national television for the first time, showing Kennedy’s head exploding and lurching backward, thanks to a bullet presumably not fired from behind him — and the skeptics had the meat for all kinds of compelling conspiracy theories.

The spice, though, took a decade longer to arrive. Jim Garrison, the New Orleans district attorney who attempted to bring charges against figures he believed to be involved in the assassination, published his third book, On the Trail of the Assassins, in 1988. Three years later, Stone turned Garrison’s book into a movie that grossed over $200 million and was nominated for eight Oscars.

He wanted only to make a political thriller. Instead he started a movement. Stone’s detractors claimed the movie handled the evidence unfairly and exhumed a moment in American history that ought to have remained buried. But Kevin Costner’s vivid portrayal of a dogged Garrison resonated with so many that Congress passed the JFK Records Act in 1992. The JFK Records Act spawned the Assassination Records Review Board, which released over three million once-classified pages to the National Archives within the next six years.

And the silver-screen drama mobilized the rank-and-file, too. Dozens of all-the-way grown men — the type who would groan having to take their granddaughters to see the newest boy band — huddled around Stone after his talk at the conference to pose for cellphone selfies. More than half of the attendees I talked to credited Stone’s movie with sparking their freelance quests for the truth about the events of Nov. 22, 1963. Even John McAdams did.

Estate of Jacques Lowe Jacques Lowe captured this portrait of the Kennedys with their daughter, Caroline, during his first session with the family in the summer of 1958. Read more about Jacques Lowe’s Rare (And Recently Restored) Photos at JFK on LightBox.

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Let’s put aside for now the people who believe he’s Langley’s stooge. McAdams’s critics still have a point, at least on one count: What could this man possibly want with JFK? He’s not a historian; he’s a political scientist. He had no particular admiration for Kennedy, or really any president, during his formative years: “I wasn’t a huge admirer of anybody, Kennedy, Johnson, Nixon. I sort of liked Ford.”

So, looking for answers, I decided to take the debunker for a spin. You know, I’ve been won over by a lot of what I’ve heard this weekend. Oswald had so many connections to this world.

“What kind of connections?” he asks.

Well, the CIA was watching him—

“Careful, careful!” he says. “I see it this way: Oswald did some things that created bureaucratic documents. He goes to Moscow and defects. So that creates some documents. The documents end up in the CIA’s files. Then he re-defects, and that creates some more documents. FBI interviews him, that creates some documents. He has a run-in with anti-Castro Cubans in New Orleans, that creates some documents. He has a file, there’s no doubt about it.” But the buffs want people to believe the CIA had agents who were obsessed with Oswald, and that, he said, is bunkum.

I tried him on a handful of other topics; each time, he laughed me off and said his opinion on what happened at Dealey Plaza had not shifted one bit.

McAdams doesn’t see any great stakes here. To him, it’s all sport. “It’s a hobby. Shouldn’t it be fun?”

But fun was not the conference’s dominant mode. Darkness — think of this great dead man, his fatherless children, the nation’s shattered hopes, and the sinister conspirators who got away with it — hung over it all. The Warren doubters want to slice through that pall by bringing the coup d’état’s perpetrators to justice.

The commission’s defenders want — well, what do they want? Some, like Max Holland, consider the further perpetuation of conspiracy theories a nuisance to the republic. McAdams doesn’t think that way. Instead he finds his thrills and his power in his ability to disillusion a new generation, to pass the torch, as it were. There was no conspiracy. This young president had promise (although not as much as you think!), and one reckless man killed him. Sometimes that’s what happens. His vision was even darker than the presenters’.

On the last day of the conference, Lisa Pease, the researcher from Los Angeles, came up to McAdams, the man she called a CIA plant, to give him a hug. He was taken aback by her friendliness.

“John,” she told him. “I’m here because of what you did. Everything you did and said to me on those message boards was so mean and nasty. I probably would have moved on otherwise, but I just couldn’t let you win.”

McAdams smiled and said, “I think we’ve all ruined each other’s lives.”