Back in the summer of 2016, in a world that never truly countenanced the real specter of a Trump presidency, the populist-nationalist troll Milo Yiannopoulos was kicked off Twitter for harassing the comedian Leslie Jones. At the time, many wondered what had taken so long, or whether the popular Breitbart editor might see his influence in the darkest corners of the shit-stirring fringe of right-wing conservatism decline. Instead, Yiannopoulos announced a new social-media comeback. “I’m joining Gab today—my username is @m. Come say hi,” he wrote on Facebook, adding that this new platform was giving out “10,000 new invites to celebrate my arrival.”

Yiannopoulos’s embrace of Gab was a coup for the nascent platform, then barely two months old, which appeared to be a better designed, less sketchy member of the growing universe of so-called “alt-right” Web sites, including Steve Bannon’s Breitbart News; Daily Stormer and Vdare, with their anti-Semitic overtones; and 8chan, the anonymous image board full of Pepe the Frog memes. Gab.com’s logo was a cutesy little graphic frog face—a seeming nod to Pepe, but described by its C.O.O. to Vice as “a biblical reference to the ‘plague of the frogs,’” which would rain down “revenge against those who went against mainstream conservative voices on the Internet.”

Yiannopoulos’s own attempt at mainstreaming failed miserably, thanks to numerous scandals and self-inflicted wounds, but he remains one of the most popular figures on Gab, despite—or, rather, due to—his reputation as a white-nationalist sympathizer. Even without Yiannopoulos as a leader, Gab has become a welcome haven for his ideas, which in the following two years became a notorious redoubt for a wide spectrum of far-right pot-philosophizing, from pro-Trump nationalists to outright white supremacists and neo-Nazis. The site soon grew a small but steadfast following, increasing its membership virtually every time a popular far-right figure—such as white nationalist Richard Spencer, or MTV host-turned-Holocaust denier Tila Tequila—got de-platformed elsewhere and moved their online presence to Gab.com. It became a cause célèbre for anti-social-justice-warrior media icons such as Ann Coulter, and received increasing support from figures like Tucker Carlson, who drew criticism after interviewing Andrew Torba, the Silicon Valley programmer who founded Gab.com, on his show. (Naturally, the backlash to Carlson’s interview prompted Breitbart to accuse his critics of being anti-free speech.) But in the past week, Gab has become known as the social media base for a man who committed what is believed to be the deadliest act of anti-Semitism in American history.

Before he opened fire inside the Tree of Life synagogue in Pittsburgh, killing at least 11 people who had gathered for Shabbat services, Robert Bowers, the alleged shooter, found a safe space to express the anti-Semitic hatred that was consuming him. “There is no #MAGA as long as there is a k*** infestation,” Bowers wrote on Gab.com. On Twitter or Facebook, Bowers’s views would have gotten him banned; on Gab, he fit right in. “Jews are the children of Satan,” read his profile. And toward the end of his post history—filled with even more violent, anti-Semitic and anti-minority content—he increasingly indicated that he would start acting soon. “I can’t sit by and watch my people get slaughtered,” Bowers wrote on Saturday. “Screw your optics, I’m going in.” Moments later, he began his shooting spree.

Law-enforcement authorities quickly zeroed in on Gab.com, and in the process, the obscure new face of right-wing extremism revealed itself. When the site launched, Torba touted his innovation as one of the last bastions of free speech: “Gab is not FOR any particular group of people, political leaning, race, beliefs, or anything,” he declared, around the same time Yiannopoulos was kicked off Twitter. “Anybody is welcome to express themselves on Gab.” In practice, however, the site quickly became a safe space for the racist expressions that got users kicked off of Facebook and Twitter. Its blind commitment to so-called free speech permitted any sort of discussion to thrive, even if it was hateful, violent, or anti-Semitic in nature. In a Vice article from April, writer Tom Bennett described his experience signing up for the site. “A quick scroll down the Twitter-like home page and I was met with a picture of Joseph Goebbels, quotes from Mein Kampf, pro-gun and anti-trans memes, and a series of posts by former B.N.P. leader Nick Griffin. This was before I’d followed anyone, reposted anything, or been active in any way. This home page wasn’t based on any preferences of mine that Gab’s algorithm had learned—it was a selection of posts that were popular with other users.”