Sam Eaton:

It's dusk on the eastern edge of the Amazon rain forest. This is a hot spot for illegal logging. And for these Guajajara Indians, patrolling their ancestral lands, the day is far from.

The spotter sees an empty canoe on the riverbank. We pull up to next it and move quickly up a narrow path into the forest. Someone just passed here, the branches showing fresh cuts from a machete. And then, just ahead, we hear their voices coming down the path.

The Guajajara Indians, armed and in full camouflage, crouch down for an ambush. Three boys from the settlement across the river, just outside the Caru indigenous territory, where the Guajajara live, they confess to cutting trees in the Guajajara's forest to make and sell charcoal, a valuable trade in this impoverished region of the Amazon.

They're taken back to the boat and then up the river to the Guajajara's camp for questioning. These vigilante patrols began six years ago as a way to battle the region's powerful logging mafia. They call themselves the Guardians of the Forest. It's dangerous work.

The land they're protecting is part of a mosaic of indigenous territories that hold nearly all of the remaining forest in Maranhao State, one of the most violent and lawless regions in the world.

Claudio Da Silva, the leader of the Guardians, says he's received dozens of death threats.