Forty-nine people are dead and 20 more injured after terrorist attacks on two New Zealand mosques Friday. One of the alleged shooters was a white man who appears to have announced the attack on the anonymous-troll message board 8chan. There, he posted images of the weapons days before the attack, and an announcement an hour before. On 8chan and Twitter, he also posted links to a 74-page manifesto, titled “The Great Replacement,” blaming immigration for the displacement of whites in Oceania and elsewhere. The manifesto cites “white genocide” as motive for the attack and calls for “a future for white children” as its goal.

The person who wrote the manifesto, identified by authorities as a 28-year-old Australian named Brenton Tarrant, also live-streamed one of the attacks on Facebook; Tarrant appears to have posted a link to the stream on 8chan before carrying out the attack.

It’s terrifying stuff, especially since 8chan is one of a handful of sites where disaffected internet misfits create memes and other messages to provoke dismay and sow chaos among the “normies” outside their ranks, whom they often see as suckers at best, oppressors at worst. “It’s time to stop shitposting,” the alleged shooter’s 8chan post reads, “and time to make a real-life effort post.” Many of the responses, anonymous by 8chan’s nature, celebrate the attack, some posting congratulatory Nazi memes. A few seem to decry it, even if just for logistical quibbles. Still others lament that the whole affair might destroy the site, a concern that betrays its users’ priorities.