Police found the heads of four men Thursday in an Indian area in the western Mexican state of Michoacan, where investigators have been searching for clandestine graves, state prosecutors said.
The heads, which were inside plastic bags and a sack, were left near a Catholic church in Zacan, a community outside the city of Los Reyes, the Michoacan Attorney General's Office said.
Federal security forces found two human heads Monday in Antunez, another community in Michoacan.
Police are digging in two fields located between Los Reyes and the city of Tinguindin, where investigators suspect there are two clandestine graves containing at least 24 bodies.
Officials began the search after a hitman, identified only as "El Marino" and suspected of burying the bodies, gave a statement to investigators, Estanislao Beltran, leader of one of the vigilante groups formed to fight the Caballeros Templarios drug cartel, told Efe.
The suspect, who was captured following a shootout between cartel gunmen and vigilantes in Los Reyes, told investigators that one of the mass graves contained the burned bodies of 19 people and the other the remains of five people killed by drug traffickers.
The Federal Police on Wednesday arrested a man suspected of disposing of bodies for the Caballeros Templarios.
Jesus Sanchez Huerta, known as "Chucho the dismemberer," was detained in Apatzingan, the cartel's main stronghold.
Los Caballeros Templarios, a gang founded in December 2010 by former members of the La Familia Michoacana cartel, deals in both synthetic and natural drugs.
The gang commits murders, stages kidnappings and runs extortion rackets that target business owners and transport companies.
The cartel uses Michoacan's 270 kilometers (168 miles) of coastline to smuggle chemical drug precursors for the production of synthetic drugs into Mexico.
Civilians began arming themselves a year ago to fight the Caballeros Templarios, which operates across Michoacan.
The federal government deployed soldiers and police in Michoacan on Jan. 13 in an effort to end the wave of violence in the state.
Dionisio Loya Plancarte, one of the cartel's top leaders, was arrested by federal forces late last month. EFE