"The first website I came to was the Council of Conservative Citizens. There were pages upon pages of these brutal black on White murders. I was in disbelief. At this moment I realized that something was very wrong," reads the manifesto, which the FBI said likely belonged to Roof.
Outbreaks of violence from groups like the KKK are rare, but the dawn of the Internet has allowed for more self-radicalization, Potok warns. And lone-wolf crimes are among the hardest to track.
"A lot of crimes are not committed by card-carrying members of these groups at all," says Mark Pitcavage, the director of the Anti-Defamation League's Center on Extremism.
According to a report by the SPLC, of the 60 successfully executed or foiled domestic-terrorism plots planned between April 2009 and February 2015, 74 percent of them were organized by lone wolves and 90 percent were carried out by just one or two people.
As is the case for any advocacy group, social media, web forums, commenting sections, and websites have emerged as key education and recruiting tools for the white-nationalist movement. Experts say that as white nationalists' views are increasingly marginalized in American culture, sympathizers retreat to parts of the Internet, where they may be free from criticism and where factions within the movement connect with sympathizers across the globe.
"The social cost of being associated with these groups has grown very rapidly," Potok says. "The net has become the first language for a whole cohort of people, especially young people like Dylann Roof."
The SPLC still says the sheer number of hate groups has grown over the last several years, but more growth has still occurred online. As of 2014, SPLC identified 764 hate groups within the United States. Roughly 115 listed on the website are active white-nationalist groups, 72 are Klan chapters, and 119 are racist skinhead organizations.
Yet, for many individuals, the anonymity of online comment sections and forums like Reddit and Stormfront provides a safer space to project controversial thoughts on race. SPLC says that Stormfront—the forum founded by former KKK member Don Black, which claims to be "the voice of the new, embattled White minority!"—has 300,000 registered users, far more than the number of people who are thought to belong to any Klan or formal white-nationalist group. On forums, writers post about the need to "PROHIBIT black music from our ears as much as humanly possible while replacing that garbage with pro white music" and express concerns about the "insane non-white immigration that is changing the composition of the United States, from what it was."
Jared Taylor, a self-proclaimed "race realist" who acted as a spokesman for the Council of Conservative Citizens following the Charleston shooting, says his own group and magazine does not use the Internet any differently than other interest groups, but he also does not believe claims that Roof was influenced to commit violence by the Internet.