8chan has been run out of the Philippines by Jim Watkins, a United States Army veteran, since 2015, when Mr. Brennan gave up control of the site.
The site remains nearly completely unmoderated, and its commitment to keeping up even the most violent speech has made it a venue for extremists to test out ideas, share violent literature and cheer on the perpetrators of mass killings. Users on 8chan frequently lionize mass shooters using jokey internet vernacular, referring to their body counts as “high scores” and creating memes praising the killers.
Mr. Brennan, who has a condition known as brittle-bone disease and uses a wheelchair, has tried to distance himself from 8chan and its current owners. In a March interview with The Wall Street Journal, he expressed his regrets over his role in the site’s creation, and warned that the violent culture that had taken root on 8chan’s boards could lead to more mass shootings.
After the El Paso shooting, he seemed resigned to the fact that it had.
“Another 8chan shooting?” he tweeted on Saturday. “Am I ever going to be able to move on with my life?”
Mr. Watkins, who runs 8chan along with his son, Ronald, has remained defiant in the face of criticism, and has resisted calls to moderate or shut down the site. On Sunday, a banner at the top of 8chan’s home page read, “Welcome to 8chan, the Darkest Reaches of the Internet.”
“I’ve tried to understand so many times why he keeps it going, and I just don’t get it,” Mr. Brennan said. “After Christchurch, after the Tree of Life shooting, and now after this shooting, they think this is all really funny.”
Mr. Watkins did not respond to multiple requests for comment.
In the early days of 8chan, Mr. Brennan defended the right of 8chan users to post anonymously, without censorship. And he dismissed incidents of harassment or violence by users of the site as the price of being an open forum.