West Virginia State Police arrested a suspect after they say they found human remains in a camp in a remote corner of the state.
The camp, at a former slave camp, was discovered in December, and was filled with about 300 human skulls.
A police spokesman told the AP the discovery was a crime scene.
Authorities say it was likely an illegal gathering of people who were locked up and left to die of starvation and disease.
The West Virginia Department of Corrections says it has begun working with local authorities to determine how many bodies may have been buried there.