SAN ANTONIO - A Frio County sheriff's deputy fatally shot an unrestrained prisoner who attacked him while being taken to a hospital for a mental evaluation.

San Antonio police say Deputy Roger Salinas suffered facial and head injuries in Monday afternoon's attack while driving his patrol vehicle on Interstate 35.

Sgt. Gabe Trevino says Salinas was able to fire one shot, striking the prisoner who was in the front seat of the vehicle.

San Antonio police say 19-year-old Andres Gutierrez was dead at the scene.

Police say Gutierrez was being transported to a San Antonio hospital for a psychological evaluation related to an emergency detention.