The body of Heriberto Cerda, the police chief in Agualeguas, was found on the bed of a patrol pickup truck, which was left on a dirt road in the nearby town of General Trevino. His head was on his lap, said a spokesman for Nuevo Leon state prosecutors who spoke on condition of anonymity because he was not authorized to discuss the case.
The body of the chief's brother, Jesus Cerda, was found inside the truck, the official said. He didn't say how Jesus Cerda was killed.
Nuevo Leon state secretary general Javier Trevino told reporters that Cerda and his brother had been reported missing Thursday.
The windshield and driver's door of the patrol car had "C.D.G.," an acronym for the Gulf drug cartel, written in blood, photos showed.
The border state of Nuevo Leon, where Agualeguas and General Trevino are located, has seen an upsurge in violence that authorities say is the result of a turf battle between the Gulf cartel and the Zetas, the cartel's former hit men.
The slayings came a day after Mexican marines on patrol in the Nuevo Leon town of Cerralvo came under fire after ordering a convoy of gunmen traveling in six vehicles to stop. Six of the assailants were killed.
In the northern state of Sonora, gunmen in a pickup truck fatally shot the deputy police chief and his bodyguard in the city of Nogales, which sits across the border from the Arizona city of the same name, authorities said Friday.
Sonora state police said gunmen opened fire on the victims with Kalashnikov rifles Thursday night.
Late Friday, gunmen opened fired on a hotel in downtown Ciudad Juarez where federal agents stay, killing one and wounding two, authorities said.
Enrique Torres, a spokesman for Chihuahua state police, said the assailants shot into the hotel's restaurant. Hours earlier, a state investigator was shot to death in a residential area, Torres said.
Ciudad Juarez, which is across the border from El Paso, Texas, is the most violent city in Mexico.