Three years ago, Richard Gage says, he was just a run-of-the mill architect, designing steel-frame buildings for clients in the San Francisco area. In March, 2006, that changed: While flipping through stations on his car radio, he caught an interview with David Ray Griffin, a retired philosophy and religion professor who calls the official account of the 9/11 attacks "one big lie."

Beginning that day, Gage became skeptical of the idea that "people living in Afghan caves" could possibly have brought down the World Trade Center. The more likely explanation, he decided, was a plot by warmongering elements within America's own government. Spreading this message is now the man's full-time job.

As radical as Gage's theory may sound to readers, it's surprisingly popular. The "9/11 Truth Movement," as it is now commonly called, has millions of adherents across the world. According to one poll, 39% of Canadian respondents said they either disagree, or are unsure, that al-Qaeda was responsible for 9/11.

What makes Gage stand out from the millions of students and young activists who comprise the bulk of the Truther community is that he is an architect -- and a respectable-looking middle-aged one at that, complete with suit and tie and receding hairline. His group, Architects & Engineers for 9/11 Truth, even scored a booth at the upcoming American Institute of Architects conference in San Francisco.

Last Saturday, I went to see Gage speak at a Montreal event hosted by the Mouvement montrealais pour la verite sur le 11 septembre, along with about 150 others (not a bad crowd, given the $10 cover charge, and the fact it was a hockey night). As part of my research for a book I'm writing on the Truther movement, I've gone to see a variety of events like this -- but none of the speakers I've seen are as lucid as Gage.

Truthers often are prone to rambling: Your average speaker at a 9/11 Truth event, taking the podium with an overflowing sheaf of Internet printouts, might start his presentation on the mechanics of the WTC attacks, segue into a denunciation of George W. Bush's war crimes and then veer into a lengthy disquisition on the 1995 Oklahoma bombing, before bringing the audience back to the Twin Towers. Not Gage: His singular focus -- laboriously examined in a 527-slide PowerPoint presentation -- is the sequence of events leading to the collapse of the World Trade Center buildings. Expertise is critical to the mission of Architects & Engineers for 9/11 Truth, he says. "We're building and technical professionals," Gage told the audience. 'We're not conspiracy theorists."

Much of Gage's two-hour-plus presentation was dry and technical -- including a seemingly endless series of slides analyzing the chemical composition of the WTC debris (an inquiry central to his claim that the Twin Towers were brought down from within by a particular type of iron-oxide-based explosive). But he also has plenty of videos embedded in his slides. And this is where the crowd came alive.

In one particularly effective segment, he put up shots of the localized fires that broke out in the lower floors of WTC Building 7 hours before it collapsed. Seconds later, he shows footage of Beijing's Mandarin Oriental hotel -- which suffered an epic top-to-bottom conflagration in 2009...and remained standing.

It's a cinematic juxtaposition that plays to the Truthers' strongest card: Even architects and engineers who've never heard of Richard Gage will concede they aren't quite sure why WTC 7, a fairly typical tube-frame structure located about a football field away from WTC 1, would be struck down by localized fires and random debris.

As one would expect, it was a friendly crowd to begin with. Before beginning his presentation, Gage polled the crowd on their views. Five people -- including me and my guest -- said they believed the "official theory" of 9/11. Ten others said they were "unsure." Everyone else -- 90% of the crowd -- said the WTC came down through "controlled demolition."

The presentation only made the balance of opinion in the room more lopsided. There were emotional gasps and shouts when some dramatic bit of evidence was displayed. A couple sitting behind me seemed particularly moved. "How can those war criminals look at themselves in the mirror after what they've done," one exclaimed. (She wasn't talking about al-Qaeda.) Even my own guest, a conservative-minded woman who normally laughs off this sort of thing, seemed transfixed, falling silent at points where I expected she'd be chortling and eyeball rolling.

During the Q&A, high passions caused the proceedings to turn nasty: When I took the mic and asked how such a massive conspiracy, presumably involving hundreds if not thousands of insiders, could possibly go undetected, the crowd began shouting me down. "Educate yourself," one audience member screamed after someone at the podium outed me as a journalist. "Typical media bullshit," yelled another.

On the other hand, I protested, at least I'd shown up in the first place -- the only working mainstream journalist (to my knowledge) in the room.

I'd hoped this would count for something: One of the Truthers' biggest complaints is that they are ignored by the mainstream media. No major media outlet has done a truly comprehensive profile or investigation of the Truther movement -- which is what led me to my book project in the first place.

Even if you are -- like me -- part of the majority that believes the "official theory" of 9/11, it's a mistake to ignore a movement as large and passionately championed as this one. Across North America (never mind Europe and North America), millions of people have decided that the leaders of the free world truly are murderers --or, at least, in league with murderers - who would wantonly slaughter thousands of their own citizens as a means to advance a geopolitical agenda. Isn't that something that should interest us?

And the movement is attracting new recruits, too. Once he'd finished his lengthy presentation last Saturday, Gage conducted a second poll of the room. This time, when he asked how many people supported the "official theory," mine was the only hand raised. Shocked, I turned to the friend sitting beside me.

After three hours in a room with Richard Gage, she'd changed her vote to "not sure."

Jonathan Kay