On Tuesday morning, after the shooting of five Black Lives Matter protesters in Minneapolis, a chilling video from LiveLeak resurfaced on Facebook and in news media: two armed men, in camouflage and balaclavas, spewing racist invective as they filmed themselves driving to Thursday’s Black Lives Matter protest. “We’re going to shut the camera off in a little bit,” one who identifies himself as SaigaMarine says. “We just wanted to give everyone a heads up on /pol/.” He signs off by pointing at the camera and saying, “Stay white.”

Sun This Week, a local Minneapolis paper, is now reporting that the other man in the video, BlackPowderRanger, is Lance Scarsella, a 23-year-old arrested and charged with assault for the shooting. And it’s widely believed by activists on Twitter that SaigaMarine — a YouTuber, model, and frequent poster to 4chan, the anarchic image board — is the 32-year-old Hispanic man who was arrested on Tuesday and released when police confirmed he was not at the protests on Monday night. (Two other suspects are also in custody in relation to the shooting.)

It’s unsurprising to people who’ve been reading it to hear that /pol/, 4chan’s politics forum, was invoked in this video. Media coverage of 4chan tends to focus on /b/, the site’s performatively offensive “random” board (birthplace of lolcats, Rickrolling, and more harassment campaigns than anyone can remember), but /pol/ has rapidly become the site’s most toxic community — as well as increasingly (and bizarrely) influential in online white-supremacist politics.

/b/ tends to be a stand-in for 4chan as a whole, but it’s hardly the site’s only community: There’s /v/, for gamers, for example, or /a/, for anime and manga. Each has a lively community — but none might be as devoted and intricate as that of /pol/, or Politically Incorrect, which shares /b/’s gleeful disorder and wanton offensiveness, but focuses those qualities exclusively on politics and world events.

News and politics were, in the early years of 4chan, the province of the /new/ board. But by 2011, /new/ had become too racist for even 4chan, and Christopher Poole (aka moot), 4chan’s creator, shut it down. /pol/ was created to fill the vacancy.

It’s easy to draw a direct line between /pol/ and /b/. Threads in both sections generally feature an OP — original poster — asking a seemingly sincere question and then people just yelling into the cybervoid underneath it. Nobody really speaks directly to one another; they just spout hateful things with abandon. But since /b/ has come under direct scrutiny from journalists and academics, its already-considerable underlying sense of self-awareness has increased. There’s an understanding that /b/ is under the microscope, and a consequent increase in the performance of offensiveness.

As /b/ gets too large and notorious to maintain its reputation as the web’s worst place, other 4chan boards have popped up in the news with new frequency. /k/, the firearms board on which SaigaMarine is apparently a frequent poster, is largely civil and polite (politics discussion is banned); /r9k/, a social-outcast board implicated in the Umpqua Community College shootings earlier this year, is dark and negative but mostly self-pitying. /pol/, on the other hand, is as bilious as /b/ — and has dispensed entirely with its already-thin veneer of “trolling.” People are racist and hateful on /pol/ not for attention or reaction, but because they are. It’s jeering and ironic in the manner of all anonymous online discussion, but when people are filming themselves pointing guns at the camera and saying “stay white,” it’s hard to get the joke.

Though much of 4chan’s technical structure — strict anonymity (as distinct from pseudonymity) and no archives — makes it difficult to generalize its community, it’s safe to say that /pol/ is where the most serious and committed racists on 4chan tend to congregate. To the extent that there is a shared political ideology across /pol/, it’s a heavily ironic mix of garden-variety white supremacy and neo-reactionary movements, with attendant interest in Ron Paul (who has been memed into a kind of apocalyptic prophet since losing the 2008 Republican primary), European history, and masculine strength. “Most days,” the Daily Beast’s Jacob Siegel wrote earlier this year, “/pol/ resembles nothing so much as The Daily Stormer [a notorious white-supremacist blog] with the signal to noise dial turned only slightly.”

Of course, /pol/ is hardly the only place white supremacists congregate online. There are abundant subreddits, a message board called Sheekyforums, and, of course, email.

But the Southern Poverty Law Center’s Keegan Hankes says, “[Y]ou can’t understate 4chan’s role.” He tells Siegel: “I constantly see 4chan being mentioned by the more Internet- and tech-savvy guys in the white nationalist movement. They’re getting their content from 4chan.”

After Dylann Roof killed nine black worshippers at a Charleston church in June, a thread on /pol/ had users sharing when they became racist.

The dark joke about /b/ was that it was the first place web-savvy journalists would check after a school shooting. As /pol/’s influence increases in white-supremacist and right-wing politics — and if its members keep filming themselves waving guns near peaceful protests — it might find itself with a similar dubious honor.