MORELIA, Mexico – A small-town mayor and an aide were found stoned to death Monday in a drug-plagued western state, the fifth city leader to be slain in Mexico since mid-August.

Michoacan state Attorney General Jesus Montejano said the bodies of Tancitaro Mayor Gustavo Sanchez and city adviser Rafael Equihua were discovered in a pickup truck abandoned on a dirt road near the city of Uruapan.

Montejano’s spokesman, Jonathan Arredondo, said initially that the victims were hacked to death with a machete, but the attorney general said they were killed with stones.

Arredondo said police were trying to determine a possible motive.

Tancitaro, a town of 26,000 people, is in a region where soldiers have destroyed more than 20 meth labs in the last year and several police officers have been killed by suspected drug gang members.

Last year the city council chief, Gonzalo Paz, was kidnapped, tortured and killed. Then in December, the mayor and seven other town officials resigned saying they had been threatened by drug traffickers and local police were not showing up to work.

Soon after, the department’s entire 60-officer force was fired for failing to stop a series of killings and other crimes, and Michoacan state police and soldiers took over security in the town. Sanchez was named mayor in January.

Also Monday in Michoacan, five gunmen and a marine were killed in a shootout in Coahuayana on the Pacific coast, the navy said in a statement. A second marine was wounded, and authorities were searching for more gunmen.

Coahuayana authorities canceled school and warned people to stay indoors.

The navy said another gunbattle across the country in the Gulf coast state of Tamaulipas left eight gunmen and one marine dead in the border city of Reynosa.

Meanwhile, the Defense Department said soldiers arrested a man suspected in the kidnapping and killing of the mayor of Santiago in the border state of Nuevo Leon. It said in a statement that Miguel Cervantes was arrested Monday.

In the border state of Chihuahua, gunmen broke into a police complex, subdued the guards and stole at least 40 automatic rifles and 23 handguns, police spokesman Fidel Banuelos said.

Banuelos said 10 officers who were in the building at the time were being questioned. He said it was not clear whether the assailants were members of a drug cartel.

In Ciudad Juarez, a border city in Chihuahua, the Public Safety Department announced the capture of a drug gang member who allegedly helped set up a car bomb that killed three people.

Suspect Jose Contreras allegedly killed a man and dressed him in a police uniform to lure federal agents to the area where the car bomb exploded, killing a federal police officer and a doctor who was helping the shooting victim.

Contreras is a member of La Linea gang, which works for the Juarez drug cartel, the department said in a statement.

Ciudad Juarez, across the border from El Paso, Texas, has become one of the world’s most dangerous cities amid a turf war between the Sinaloa and Juarez cartels.

(This version CORRECTS spelling of mayor’s first name to Gustavo.)