SAN ANTONIO (AP) _ One of the four people found dead inside their rigs at two area truck stops last month died of natural causes, authorities said Friday.

The Bexar County medical examiner's office has not released the cause of death for the three others.

Solved was the death of Hubert Ray Hardesty, 53, who was found Monday in a rig at the Flying J on Interstate 10 in San Antonio.

His family reported him missing after Hardesty, a driver for Watkins Truck Co., didn't arrive in Birmingham, Ala., as expected, said Brad Alston, safety director for the company.

On Nov. 1, two bodies were found dead inside a rig at the Petro Stopping Center, just west of the Flying J. Police identified them as Harry Ackroyd, 35, and Michelle Ackroyd, 32.

The medical examiner's office said a third body, identified as Byron Gonzales, was discovered inside a rig at the truck stop on Thanksgiving Day.

Police have said one theory they are investigating is whether bad drugs are being sold in the area of the stop.