For 14 years, a human skeleton known as 317-38-10 sat in a cardboard box stored in a metal shipping container on the rooftop of a building in Guatemala’s capital, Guatemala City. The number was a code, representing the place it had been discovered: 317 was the designation for a pine-forested mountaintop pocked with mass graves near a town called San Juan Comalapa. It was the 38th mass grave archaeologists excavated in the country, and the 10th body unearthed in that grave.

Outwardly, there was nothing particularly special about it. Like all skeletons, many of the defining physical features that made its owner unique in life—hair, skin, eyes, and other soft tissue—were all gone, leaving only the bones and the basic information