Last week a photographer for the Minneapolis Star Tribune filmed a border patrol agent approach a protester, lying prone in the street, and aim a canister of pepper spray at his eyes. The protester was already detained, three other agents pressing his body into the pavement, but the agent can nevertheless be seen spraying the orange chemical irritant, which causes excruciating pain, at point-blank range.

The agent probably thought he would enjoy anonymity for this bit of brutality. The federal police terrorizing Minneapolis remain largely nameless as they dole out horrifying – and in two cases, fatal – violence against anyone opposing Operation Metro Surge. But within two hours of the Star Tribune posting the footage to social media, a group called Pacific Antifascist Research Collective claimed to have identified him.

The collective – which days earlier promised in a post to “identify ICE terrorists until ICE’s campaign of terror is stopped and the armed thugs and their leadership are held accountable” – made flyers of the agent’s face for people to share online, or to print out and tape to telephone poles and buildings across Minneapolis.

“TYLER GRAMLIN”, screamed the text on the flyers in English, Spanish, Hmong, Somali and Tagalog. “SUSPECTED KIDNAPPER/TERRORIST”.

The Pacific Antifascist Research Collective did not publicly share the methods it used to identify Gramlin, but I know its research to be reliable. Its activists follow exacting editorial standards, a tendency born from the desire to be trusted by their communities; any missteps can destroy the credibility of the whole project. The collective describes itself as an “autonomous group” of “researchers dedicated to providing communities from the Rockies to the Pacific with research and tools to protect themselves from fascism in all its forms”. Its members, like most of the 60 or so other antifascists I talked to for my new book, To Catch a Fascist: The Fight to Expose the Radical Right, keep their own identities a secret to prevent reprisals from the far right.