One of the masterminds behind an arson attack on a casino that killed 52 people last year was killed in a gunbattle with soldiers Wednesday.

Suspect Franisco Medina Mejia was among the four gunmen killed during the confrontation on a highway near the border city of Nuevo Laredo, across from Laredo, Texas, the Defense Department said in a statement.

The army said the dead suspects had eight rifles and a grenade launcher. One of the bodies had old burn wounds and one of the rifles was engraved with the words "El Quemado," or "The Burned One," Medina Mejia's nickname. He was allegedly a top aide to Zetas leader Miguel Angel Trevino, and also allegedly killed Manuel Farfan, a retired general who served as the police chief of Nuevo Laredo in 2011.

The arson attack on the casino was allegedly the work of the Zetas drug cartel. On Aug. 25, gunmen stormed into the casino building, spread gasoline and set the building on fire, trapping and asphyxiating dozens of people.

Other suspects arrested previously and accused of ordering or carrying out the attack have said the cartel targeted the casino because its owners hadn't paid extortion money, a theory officials confirm. At least one of the casino's owners has denied the claim to reporters.

Also on Wednesday, prosecutors in the western Mexico state of Michoacan said a total of nine gunmen have died in two confrontations with the Mexican army.

Five male suspects died in a shootout Wednesday after they opened fire on a military patrol outside an old hacienda in the township of Churintzio.

Two assault rifles, pistols and other weapons were found near the suspects' bodies.

Four other men were killed in a sport utility vehicle late Tuesday. Three of the suspects had been carrying assault rifles.

Michoacan is home to the Knights Templar drug cartel.