The recent murder of a rights activist assigned to protect isolated tribes in far western Brazil has raised fears for the security of the Amazon’s indigenous populations and those who defend them.

The worker, Maxciel Pareira dos Santos, was shot and killed on September 6 by an unidentified hit man riding on the back of a motorbike along the main street of Tabatinga, a frontier city near sprawling Javari Valley Indigenous Territory. The protected area harbors the largest concentration of uncontacted and isolated tribes in the world.

Santos had worked for 12 years for Brazil’s indigenous affairs agency, FUNAI, manning a strategic outpost where two rivers lead into the depths of the 33,000-square-mile reserve, with its estimated 5,000 indigenous inhabitants. The post