“Now you have this new ironic world of killers,” said J.J. MacNab, a fellow at George Washington University’s program on extremism. “It’s a different world — just a constant flow of bad statistics, bad memes, bad lies about the people they want to hate.… That’s the 4chan way: You say things that are outrageous that you don’t necessarily believe — and over time you come to believe.”

Unlike the white supremacists of old — from the Ku Klux Klan to newer neo-Nazi terror groups such as the Base or the Atomwaffen Division — the new recruits to racist 4chan and 8chan forums are often teenage boys in high school, MacNab said. They act out their rage at a time of dimming economic opportunity for some young people and the changing demographics of a country they have been told no longer has a place for them.

“They piggyback on each other’s crimes and, as each one became more famous, then just absolutely made it more desirable for them to copy,” MacNab said. “The joke is always: Who can beat the kill number? … To them, it’s like a video game. How do you score better than the last one?”