Last month, residents of the McAnulty Acres apartment complex in Pittsburgh thought little of the quiet truck driver Robert Bowers.

Later, they’d tell the American press he seemed entirely normal. He was 46. He had dull blue eyes and thin greying hair. He kept to himself but would say hello if they passed him stood outside smokingor on the way to his first-floor apartment.

What his neighbours didn’t know was that online, Bowers possessed a very different personality. On his Gab social media account, he was obsessed with antisemitism, fervently posting vicious hatred of Jewish people.

On the morning of Saturday 27 October, Bowers logged into Gab, sharing a barrage of other people’s antisemitic posts, conspiracy theories and a racist cartoon, before writing his own message. Targeting HIAS, a Jewish NGO which supports refugees, he finished the post with the words: “Screw your optics. I’m going in.”

Minutes later, police say, he walked into Pittsburgh’s Tree of Life Synagogue, armed with an assault rifle and three handguns, and killed 11 people.

Gab’s place in the worst antisemitic violence in modern American history has drawn focus to a parallel online world where the far-right thrives. As Facebook and Twitter come under increasing pressure to crack down on extremism, “free speech” alternatives have emerged. The alt-right is trying to create its own online eco-system; toxic eco-chambers where racist, antisemitic, anti-Muslim, anti-liberal messages can spread un-checked.

Patrik Hermansson, researcher at anti-fascist organisation Hope not Hate, says people who spend time on these alternative sites have usually been radicalised elsewhere first, sometimes on mainstream social media.

“On mainstream sites, they might get invited or pushed onto alternatives,” he says. “It’s still not a completely separate sphere, but it’s complimentary.”

When Trump supporter Andrew Torba set up Gab, it was an attempt to counter what he called “the entirely left-leaning Big Social monopoly” of companies like Facebook and Twitter. Back in 2016, Conservatives were calling out the tech-world for its left-leaning bias and Torba wanted to offer them an alternative—a social network with fewer rules. “We’re not going to police what is hate speech and what isn’t,” Torba told Wired in the same year.

From the beginning, Gab’s reputation for “free speech” attracted neo-nazis and people who had been banned for using racist language on more mainstream sites. Former Breitbart-writer, Milo Yiannopolous was an early adopter after Twitter banned him for life. On Facebook, his followers celebrated Gab’s lack of “censorship”, they saw it as freedom from “social media fascists” that “pander to the left.”

Torba was not the only entrepreneur to see opportunity in these attitudes. While Gab became an alt-right version of Twitter, Rightpedia became the alt-Wikipedia and Voat the alt-right’s Reddit—alongside 4Chan’s ‘politically incorrect’ thread, the alt-forum.

Ray Vahey’s Bitchute, a sort of alt-YouTube, sells itself as somewhere creators can “express their ideas freely” and Voat’s tagline is “no censorship.”

Alt-web sites tend to replicate the mainstream internet, just without such strident rules. And their racism is getting worse. A September study by Princeton University’s Network Contagion Research Institute found that racial and ethnic slurs were becoming more popular in fringe web communities.

Bowers’ own Gab profile reflected the slew of antisemitic language, memes and conspiracy theories that exist in the alt-web. He posted again and again about the same “white genocide,” the irrational, racist conspiracy theory that Jewish people encourage immigration because they want to eliminate the white race.

This old, antisemitic trope has been revived by the alt-right in Europe, America and South Africa. Bowers had been so indoctrinated by the conspiracy that after his arrest at the Synagogue, he told a Special Weapons and Tactics (SWAT) officer: “They’re committing genocide to my people.”

Robert Goldberg, professor at the University of Utah and author of Enemies Within: The Culture of Conspiracy in Modern America, says repetition is key to spreading conspiracy theories online.

“When you are constantly bombarded with a message—that you, your family, your race is in trouble and that trouble is caused by a particular group—people believe, and there are many people who will act on those beliefs.”

“Because we [Americans] are armed as a nation, it’s easy to pick up a weapon and do harm.”

Critics have shrugged off the alt-web’s relevance. Its sites are buggy and its numbers are tiny compared to Silicon Valley rivals. Gab’s 250,000 active users,for example, pale next to Twitter’s 326 million.

Yet Bowers’s path from feverish antisemitism online to real life violence points to a real danger from this small core of alt-web users.

“They use language that is very de-humanising. They make violent and hateful ideas palatable. These social media platforms are particularly good at that, they help normalise it,” says Hope not Hate’s Hermansson.

“It makes you want to live up to the group identities that exist in these forums. Some will act on that but it’s not most of them.”

While alt-web sites are plagued by shutdowns by internet gatekeepers, its user base is resilient. Now Gab has been taken offline, some of its users have moved to Minds.com—a Facebook alternative with 105,000 active users according to TechCrunch.

But the alt-web does have a weak point: its funding sources.

While supporters have tried to set up alt-payment platforms such as Hatreon and GoyFundMe, it’s difficult to do business online without relying on a handful of mainstream companies that enable payments to be made.

Hatreon, for example, was set up to give the alt-right financial independence after mainstream platform Patreon started banning its figureheads and vloggers.

But the company still had to rely on Visa to process payments. After Charlottesville’s 2017 Unite the Right rally, Visa stopped giving financial services support to companies with ties to hate groups—plunging Hatreon into a state of inactivity where it remains today.

On Twitter, users like Deplatform Hate and Sleeping Gants expose companies that continue providing services to alt-right groups. In the aftermath of the Pittsburgh shooting, Deplatform Hate immediately called out Paypal and Stripe for working with Gab. Both payment platforms stoppedwithin 24 hours of the shooting.

But months before Bowers stepped into that Synagogue, Deplatform Hate had notified both Stripe and Paypal about the nature of Gab’s content.

The anonymous person behind the Twitter account—who asks for their real identity not to be revealed—says these companies fail to act in time because they are reluctant to accept the power they have.

Over the phone, the activist’s warning was stark. “Even though we told them Gab is a crazy, crazy place months ago, they only take action now. It’s going to take someone to die.”