Five sets of skeletal remains found concealed in the desert west of Tucson appear to be homicide victims, authorities said Tuesday.

Border Patrol agents found the remains May 28 about 12 miles northwest of Sells on the Tohono O'odham Reservation in an area often used by smugglers. The remains were partially covered with rocks and possibly a tarp.

"Some have broken bones, and they're not breaks that you would see after death," Dr. Greg Hess, Pima County's chief deputy medical examiner, said Tuesday. "They're likely the result of firearms and blunt-force injuries."

The bodies might have been in the desert for a year before being discovered, Hess said.

"We can't determine if they are all males yet," said Hess, adding that most of the remains appear to be adults, although an age range can't immediately be determined. "We're trying to sort it out. It's going to take us some time," he said.

Based on their clothing, they were probably not U.S. citizens, he said.

Tribal police said the five deaths were being categorized as suspicious based on conditions at the scene.

The investigation is continuing, and no other information is immediately available, Tohono O'odham Police Chief Joseph Delgado said.