A 17-year-old, Kyle Rittenhouse, was arrested and is being held in nearby Lake County, Illinois, where he lives, in connection with the shootings, according to court documents. He can be seen in multiple videos taken that night, carrying a semiautomatic assault rifle, and some videos appear to show him shooting people. It was not clear whether Mr. Rittenhouse had seen the social media appeals.
In an interview conducted that night before the shootings, Mr. Rittenhouse told a video editor at The Daily Caller, a conservative news and opinion site that he and other armed people were present because protecting businesses was “our job.”
On the day of the shooting, the Atlantic Council researchers found, a Facebook page was created, calling for people to “gear up” and protect Kenosha. One person posted on the page, which has since been deleted, “shoot to kill.”
Another now-deleted Facebook page, claiming to represent a local militia group, asked people to “take up arms” and defend Kenosha from “evil thugs” who were “planning on the next part of the City to burn.” That invitation was promoted by Infowars, leading to it being repeated on hundreds of other Facebook pages.
On a Reddit discussion thread, one poster wrote that 75 people were en route from Green Bay, adding: “We have lots of guns. Lots of pipe bombs.” Another Redditer demanded that “all non-whites and degenerates leave Kenosha.”
Facebook has removed Mr. Rittenhouse’s accounts on that network and Instagram, removed praise for him on other accounts, and blocked searches for his name, said Brian Fishman, Facebook’s director of Counterterrorism and Dangerous Organizations.
In a Twitter thread, Mr. Fishman said the company had also removed the account of the militia group for violating Facebook’s rules, but that it had found no evidence that Mr. Rittenhouse had seen the group’s posts.