Police officers guard the Tree of Life synagogue following the shooting at the synagogue in Pittsburgh.John Altdorfer / Reuters

Before a gunman opened fire on the Tree of Life synagogue in Pittsburgh Saturday morning, he posted a threat to the Jewish community online.

HIAS [a Jewish nonprofit organization] likes to bring invaders in that kill our people. I can’t sit by and watch my people get slaughtered. Screw your optics, I’m going in,” the suspect, Robert D. Bowers, reportedly wrote. Just hours later, he killed at least 10 people and wounded others in what the Anti-Defamation League has declared the deadliest against the Jewish community in the history of the United States.

Bowers didn’t make his anti-Semitic statements on Twitter or Facebook or even Reddit, but rather on a small social network called Gab. It was founded in 2016 as an alternative to Twitter and other large social platforms, and indeed looks and operates similarly to Twitter, allowing users to follow and reply to one another, and to reshare short status updates.

But while Twitter, Facebook, and other mainstream social networks abide by ever-evolving sets of community standards, Gab allows users to say pretty much anything they want. Andrew Torba, the Silicon Valley Trump supporter who created it, said that he wanted to offer an alternative to mainstream social networks, which he and others feel are biased against conservatives.

“What makes the entirely left-leaning Big Social monopoly qualified to tell us what is ‘news’ and what is ‘trending’ and to define what ‘harassment’ means?” he said to BuzzFeed News in 2016, explaining his decision to create the company. “It didn’t feel right to me, and I wanted to change it and give people something that would be fair and just.”

Since then, Gab’s maximalist approach to free speech has made the network the de facto home of extremist figures who have been booted off mainstream social networks for making threats, inciting violence, or promoting racist, sexist, and anti-Semitic ideas. While Twitter has banned extremist figures such as Milo Yiannopoulos, Richard Spencer, Alex Jones, and Andrew Anglin, Gab continues to welcome them and their followers with open arms. It has been called a “hate-filled echo chamber of racism and conspiracy theories” and “Twitter for racists.”

This has led to tension with some of the platforms hosting Gab amid increasing pressure for web companies to “deplatform” extremist groups and individuals. In 2017, the Gab app was banned from the Google Play store for violating its policy against hate speech, and in August of this year, Microsoft threatened to stop hosting the platform on its servers over similar concerns. (Microsoft did not immediately respond to a request for comment on Saturday afternoon.) Shortly after Saturday’s shooting, Gab tweeted what appeared to be a notice from PayPal, saying that the payment-processing platform would be terminating its relationship with Gab “pursuant to PayPal’s user agreement.” Opponents of deplatforming argue that censoring extremist speech, actors, and platforms doesn’t stop violence, and in fact might incite it. “Free speech is crucial for the prevention of violence,” the Gab account tweeted Saturday. “If people can not express themselves through words, they will do so through violence. No one wants that. No one.”

Over the past few years, Bowers has shared a steady stream of anti-Semitic statements on Gab, where he had a verified account. His bio on the platform declared that “Jews are the children of Satan,” and its background photo included the number 1488, which is loaded with white-supremacist symbolism.

After the shooting on Saturday, Gab issued a statement declaring, “Gab.com’s policy on terrorism and violence have always been very clear: we a have zero tolerance for it. Gab unequivocally disavows and condemns all acts of terrorism and violence. This has always been our policy. We are saddened and disgusted by the news of violence in Pittsburgh and are keeping the families and friends of all victims in our thoughts and prayers.” Bowers’s account was suspended shortly after the shooting. In its statement, Gab noted that it “took swift and proactive action to contact law enforcement immediately.”

Yet even on Saturday afternoon, anti-Semitic statements still flourished on the site. “Jews are so fragile,” declared a user by the name of @DonMAGA. Said another: “The Jews are the real terrorists and we must remember that in these trying times.” Many more shared anti-Semitic propaganda.

The company did not immediately respond to a request for comment from The Atlantic on Saturday afternoon.

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