But it was the images of the vans that drew me to him. He documented one van, then another, and a third, posting the videos to his Facebook page. The engine of one van was still running, he showed us, the coffee still warm. Ladders were strapped to the roof.

Once engines of economic opportunity, the vans are now tombstones for the disappeared. In the counties that make up metropolitan Atlanta, immigration-related arrests have spiked over the last two years, as ICE and local law enforcements agencies have moved to vigorously enforce immigration law at the behest of the Trump administration.

As Mr. Guevara’s videos reveal, a predator does indeed stalk these quiet corners and busy streets. The “wolf” arrives in the form of an unmarked car, or cars. The human target is quickly ushered into an S.U.V. by immigration agents wearing body armor.

Mr. Guevara’s job, and his obsession, is to stalk the wolf.

Doing that is hard. He was up at 5 a.m. when I joined him, on the dark roads of Gwinnett County, prowling the housing projects and gas stations that were just coming to life. He rolled down his window and asked for tips. He checked his phone for Facebook messages. His followers provide valuable crowdsourced intel.

Often, he arrives too late, after ICE has come and gone, receding with its prey into the sprawling but largely invisible apparatus of detention and deportation. If he is fast enough, he can capture an arrest as it happens.