How Police Used Antifa to Investigate Far-Right Proud Boys

The trial concerns the events of Oct. 12, when Gavin McInnes, the founder of the Proud Boys, appeared at the Metropolitan Republican Club on East 82nd Street, where he reenacted the 1960 murder of a Japanese socialist by a teenage ultranationalist. Protesters had gathered outside.

Afterward, as multiple videos show, 10 members and associates of the Proud Boys surrounded and beat four people — believed by the police to have been members of Antifa —who had circled the block to approach them.

The Proud Boys, Mr. Segal said, view themselves as defenders of conservative values and put a premium on confronting or attacking leftists. He said the group’s leaders have used bigoted language about Muslims and women and that “violence is built into the ideology,” due largely to Mr. McInnes, who started the Proud Boys in 2016.