Photographer Ross McDonnell travelled through Guerrero state, Mexi­co with an anti-drug cartel unit, armed with machetes and shotguns. But the masked men rounding up criminals in this elegant documentary short are not with the Mexican Army or the Federal Police. They’re “Auto Defensa” — vigilante groups of self-deputized campesinos who imposed a blockade on their troubled town and now patrol it.

Profiled recently by LightBox, McDonnell talks about the rising movement and it’s disconcerting developments, including “a program of social cleansing, arresting criminals and those suspected of crimes and detaining them in makeshift prisons in the Guerrero hinterlands” and shame-parading the prisoners through town. Their numbers — and the number of their prisoners — is growing.