The remains of five people have been found in the Arizona desert, and officials believe none of them were U.S. citizens.

The skeletons were found on May 28 on the Tohono O’odham Reservation, an area well-known to be a smuggling corridor to Mexico. and authorities say they were partially covered with tarps weighted down with rocks. Some of the remains had been damaged by animals, but they were positioned in a suspicious way, leading investigators to believe they didn’t die naturally.

“It’s not a typical migrant death site. Usually that’s people laying under a tree because it got too hot, and they’re on the surface of the ground and nobody tried to bury them,” Chief Medical Examiner Gregory Hess said.

It’s been reported that at least one woman was among the victims, and most of the remains showed evidence of broken bones which could have been the result of gunshot wounds or blunt force trauma. An investigation is still ongoing. Autopsies will be carried out next week.