When a gunman burst into the Tree of Life Synagogue Saturday to commit the most deadly anti-Semitic attack in U.S. history, police say he yelled four horrid, unambiguous words before opening fire — “All Jews must die.”

First responders were called only minutes later — but by the time the suspect, named by police as 46-year-old Robert Bowers, was in custody, 11 members of the congregation lay dead and six more were injured.

This shooting may have been the most violent, gruesome show of anti-Semitism in our country’s history, but the motivation behind it certainly isn’t unique — and neither was the hateful rhetoric Bowers used to justify his actions.

In fact, an obscure far-right forum called Gab, which Bowers frequented and which purportedly dedicates itself to preserving free speech, was home to exactly this kind of hateful rhetoric. It was taken down immediately after the shooting — and rightly so. While the site openly allowed hateful speech, it claimed to clamp down on threats of violence — but in Bowers case, among many others, it failed to do so.

In the hours following the attack, when Bowers’ posts were revealed to the world, it became clear that if Gab’s goal was to crack down on threats of violence, it utterly failed. Bowers posted numerous rants on the site that seemed threatening and the site didn’t flag him once.

“HIAS likes to bring invaders in that kill our people,” Bowers posted minutes before authorities were called. “I can’t sit by and watch my people get slaughtered. Screw your optics, I’m going in.”

Bowers also posted pictures of his gun collection, and said on a regular basis that Jews were a threat to white society. He was a clear threat to Jewish people — but this isn’t the first time an avid Gab user has elicited backlash for violence against minorities.

Christopher Cantwell, one of Gab’s most well-known users, achieved notoriety when he allegedly pepper-sprayed counter protesters at last year’s white supremacist rally in Charlottesville, Virginia.

Cantwell said on Gab that Saturday’s shooting was completely justified and even tossed out anti-Semitic slurs to add fuel to the fire, and he has repeatedly called for the assassination of Jews and police officers on his Gab account and on his podcast, “Radical Agenda.” If one of Gab’s most prominent users is able to get away with statements like these, clearly the site isn’t doing enough to quash legitimate threats of violence.

While the fringe forum never aimed to stir up racial animus and harbor hateful users, according to founder Andrew Torba, expecting that to happen only seems logical. A large number of Gab’s users had been banned from mainstream social media sites like Facebook and Twitter for alarming posts, and naturally flocked to a site that would accommodate their extremist views — a cornucopia of right-wing zealots who reinforced each others bigoted beliefs.

According to American University professor Susan Benesch, hateful statements like many of the ones on Gab are not a direct source of violence, but hateful language can provoke people who are already inclined toward extremism and violence — and that’s exactly the kind of environment Gab fostered.

No social media site is perfect when it comes to removing and reporting potentially violent individuals — even Facebook and Twitter, the world’s largest social networking sites, still contain ISIS accounts. But considering the vitriolic rhetoric Gab users spewed on a regular basis, the site should have been especially vigilant.

Still, the site itself isn’t 100 percent to blame for not stopping the alleged Pittsburgh gunman — small, fringe forums like Gab often go undetected by federal investigators who comb through social media trying to intercept terrorist threats.

“Mainstream fringe sites like 4chan and parts of Reddit get most of the attention, and sites like Gab fly under the radar outside of these communities because frankly they’re these isolated islands that don’t connect to the reality-based internet,” Brandon Szuminsky, an assistant professor of journalism at Baldwin Wallace University who specializes in misinformation and social media, told the Post-Gazette.

Gab’s partners’ responses to the Pittsburgh shooting were swift but reactionary. Paypal, Gab’s payment provider for premium users, stated firmly that the site wasn’t doing enough to address very real threats among its user base. GoDaddy.com, the forum’s host website, also severed ties with Gab after the shooting.

“[We have] investigated and discovered numerous instances of content on the site that both promotes and encourages violence against people,” a GoDaddy.com spokesperson said.

A Gab spokesperson passionately defended the site, saying it was purely a free speech promoter and didn’t want to be associated with any violent act provoked by rhetoric on site.

“Gab unequivocally disavows and condemns all acts of terrorism and violence,” the company said in a now-deleted post on Medium in response to Saturday’s shooting. “We clearly, directly and incontrovertibly prohibit threatening language that infringes on the safety of another user or individual.”

While the intentions behind founding the site seemed noble on the surface, the reality didn’t live up to the dream. There’s a reason Facebook and Twitter put limitations on hateful speech — it harms natural discourse and is a breeding ground for extremism.

Fringe sites like Gab are havens for extremists, who, when they put their heads together, pose a real threat to public safety. Thankfully our country has, for now, shut down one hate site — but there’s still a long way to go before we vanquish them all.

Write to Neena at [email protected]