For three years, Mario Vergara has regularly ventured into the hills of the southern Mexican state of Guerrero to search for the remains of his brother Tomás. Although he hasn’t located his brother, he’s found dozens of buried bodies. But this isn’t unusual — it’s only evidence of a much larger problem.

Vergara is part of a loose movement of buscadores, or searchers, spurred to action after the disappearance of 43 students in Iguala in September 2014. The students went missing after a confrontation with security forces, and the search for their remains resulted in the discovery of dozens of other bodies buried in mass graves.

The case of the 43 male teacher-training students blew the cover off the epidemic of forced disappearances in Mexico, where more than 32,000 people are estimated to be missing. It’s one symptom of serious and deeply entrenched issues.

In Mexico, the vast majority of crimes go unpunished, countless government officials participate in organized crime, and the police and military have been deployed in massive numbers in an ostensible fight against the cartels. The result is a country where thousands of heavily armed men — be they private actors or agents of the state — can kill with impunity.