“I’ve seen buildings collapse before,” was the first thing I heard as I took my seat. “I know what a controlled demolition looks like.”

That was Mike—who looked to be in his late sixties and wore a black panama hat over his mustache and hepcat sideburns and a guayabera shirt over his paunch—casually asserting his knowledge about buildings in freefall in a familiar but outdated New York accent to a Swede who nodded intently. We were in Brooklyn, the most Jewish borough in America’s most Jewish city, along with about two dozen other people, some of them Jewish and many habitués of the city’s left wing political scenes along with myself and what looked to be at least four other people scribbling in reporters’ notebooks, to hear an anti-Semite run down the Zionist conspiracy behind the Sept. 11 attacks.

Controversy had been building in New York’s Jewish and left wing circles and most vocally in the space where those circles overlap over the decision to invite Christopher Bollyn to expound on his belief that “9/11 is a massive Zionist Jewish crime,” as he’s written. Once a member of far-right organizations like the Liberty Lobby tied to Holocaust denial and white nationalism, Bollyn’s role inside the self-proclaimed 9/11 truth movement has given him some inroads to the left. Those roads led him this week to The Brooklyn Commons, an organizing space and event venue once associated with some of the leading lights of left-wing politics.

Posters at the Commons promised “a riveting analysis of who masterminded the false flag terrorist act known as 9/11,” from “a rare voice exposing the Neocons and their Zionist partners-in-crime.” Which seemed an unlikely pitch for a non-profit operation that had described itself as providing “resources to the progressive community.”

But under pressure from groups that have used the Commons including Jacobin, The Baffler and WBAI to cancel the event its owner, Melissa Ennen, instead posted a statement at once denying any knowledge of Bollyn’s background, insisting racism has no place in left-wing politics and invoking an anti-safe space free speech ethos as grounds for allowing him to speak. After issuing her statement, the Commons’ “about” page, which had called it a resource for progressives—was removed from its website.

Notably, Ennen didn’t mention her own longstanding ties to the 9/11 truth movement, which might have explained her intransigence and also cast doubt on her claim that she “did not research the speaker before accepting the rental.” Those details came out only when they were reported by Daniel Sieradski, the publisher of Jewschool, a site with the banner “progressive Jews and views.”

Eugene, 32, a Ukrainian-born Brooklynite wearing an Industrial Workers of the World shirt, showed up Wednesday night to protest Bollyn’s talk. He had this to say about the Ennen’s decision to host it: “For an event with a Holocaust denier talking to five people she decided to sabotage her progressive space and she decided to sabotage her reputation.”

Several left-wing organizations tied to the venue repudiated the booking, with some eventually cutting ties with the Commons because of it.

When the event started at 7, there were close to two dozen protesters outside. This group was younger, more traditional in their radical politics, and, judging from my conversations and observations, more likely to identify as Jewish than the attendees walking past them. The protesters, too, were mostly fixtures of New York’s left-wing politics and in some cases of the same small circles as their antagonists at the talk.

Here was some sampling of the left fighting with itself over the meaning and borders of its politics. Thus the multiple protesters carrying signs with variations on the slogan, “yet another Jewish anti-Zionist against anti-Semitism.”

One such sign was held by Rosa, an “almost 40” cultural worker living in New York and active in anti-Zionist politics aimed at Jewish audiences.

“Free speech is the principle that the government should not ban people from talking,” Rosa said in response to Ennen’s defense of booking Bollyn. “There is no obligation for anyone to provide a platform for bigotry, Holocaust denial, anti-Semitism etc. Even as a bad excuse it doesn’t register on the scale.”

Also protesting was Mal, a New Yorker who did not give her age but appeared to be in her late twenties and said she was involved in left-wing anti-authoritarian and LGBT politics.

Anti-Zionism is not a form of anti-Semitism, Mal argued, but “it is used as a cover for anti-Semitism and we do need to be vigilant but the thing is we’re seeing it in more parts of the left.” Where else had she seen it? “Occupy circles.”

She elaborated: “I’m talking about casual use of anti-Semitic tropes and anti-Semitic propaganda like the concept of Rothschild Zionism being what’s undergirding the economic oppression of the working class.

“Giving these people a platform in a leftist space is unconscionable” Mal told me. “Because what is leftism anymore if you are condoning anti-Semitism? What is that anymore? You’ve completely lost the plot, then.”

Inside, past the coffee and wine bar, the crowd seated in the back was a bit older and more visibly diverse. Rudy Dent, a black retired New York City firefighter who says he worked on the pile at Ground Zero and is a minor celebrity in anti-Semitic 9/11 conspiracy circles in his own right, was there to introduce Bollyn. There was more visible political diversity, too, among those seated inside, with Palestinian solidarity activists beside dedicated 9/11 truthers, and hippie washouts stuck in a conspiracy loop beside a man who said he drove in from Massachusetts for the talk where he sported a pin with the image of Syrian dictator Bashar al-Assad beneath the slogan “long live the Syrian Arab Republic” and held a poster with Stalin on one side, Putin on the other and between them the words, “Restore Socialism Reunite Soviet Union.”

Not long after the talk started, people stared to nod off. Yes, it was an older crowd. But even if you wanted to stay awake just to stoke your,outrage it was difficult. Ever sat through a two-hour PowerPoint presentation?

Strip away everything else and here was a middle-aged man dully clicking through slides. This slide has Jewish names and Zionist written across the forehead of some demonic figure; this one Menachem Begin; this one details on a German journalist’s allegedly suspicious marriage to an Israeli official; this one the iconic picture of five-year-old Omran Daqneesh, a Syrian child whose face covered in blood and ash after he survived a bombing, shown here supposedly as some proof of something or another to do with the Zionist criminals and 9/11 and the long con that is all of history as underwritten by the unseen—except to Bollyn and his ilk—Jewish hand. The presentation was supposed to be an hour followed by questions, but it droned on for nearly the full two allotted for the event.

The only bit of comedy came from Bollyn’s exaggerated pronunciation of foreign words and names, like Jab-oh-teen-skee instead of Jabotinsky as if that gave him a scholarly air.

There was no formal intermission but at one point a protester interrupted the talk by calling Bollyn a fascist with ties to neo-Nazis and was pulled out of the venue by the security guy in the room, prompting the woman who had been collecting tickets for the event to remark with evident disgust: “Look at what the Palestinians have to put up with.” A second incident that I did not witness involved a protester being cursed at and then spitting on a Commons employee, which led to four police cars showing up and the arrest of one protester outside after that person called a police officer a “pig.”

The night ended with mutual recriminations and recording devices as the attendees crossed paths with the protesters on the sidewalk.

Among the protestors, no one expressed surprise that Bollyn existed or that ideas like his found an audience but they didn’t seem to understand exactly how the hell he had wound up here, invited into Brooklyn by someone many of them knew, at a left-wing cafe in a long-since gentrified part of town.

Mike, who knew all about controlled demolitions, dropped a bit of Yiddish when he was confronted by protesters leaving the talk. What had he been doing there, I asked him after that exchange. Just keeping an open mind, he said, the same answer I heard from two other people who had been inside and maintained after two hours of slides that it was all very intriguing but they hadn’t formed any opinions on it yet, and also it wasn’t like he’d said all Jews are bad, or all Zionists as the case may be. Mike, expressing a common sentiment among the open-minded, said he didn’t necessarily believe everything Bollyn said but he didn’t believe the government’s account of 9/11 either.

Of course “just asking” can become its own statement, as Donald Trump has demonstrated. In the cavity of 9/11 conspiracies, and conspiratorial thinking more generally, there is often an obsession with Jews and Jewish power.

And where Bollyn is widely considered a fringe figure, his line of thinking has found more mainstream messengers in figures like Kevin Barrett, the University of Wisconsin professor who also suspects 9/11 was an inside job pulled off by Zionist agents and dabbles in Holocaust denial, or more recently Oberlin College’s Joy Kargea, who credits the Jews with not just 9/11 but also the rise of ISIS and the Charlie Hebdo murders. As she explained on Facebook: “I stopped letting people bully me with that ‘You’re being anti-semitic’ nonsense a long time ago.”

“If you listen,” Mal said, “to the kind of 9/11 truth-adjacent and Alex Jones-adjacent sections of the left, you will see a lot of this and you will see it as a pervasive thing.”