Authorities have identified the four men whose severed heads were found in an area of western Mexico where investigators have been searching for clandestine graves, the Michoacan state Attorney General's Office said.
The heads are those of four Purepecha Indians: Bulmaro Herrera Rincon, 55;, brothers Alejandro and Noe Alvarez Gonzalez, 22 and 24, respectively; and a fourth man identified only as Juan, the AG's office said.
The heads - placed in individual plastic bags inside a sack - were left near a Catholic church in Zacan, a community outside the city of Los Reyes.
The four went missing in the early hours of Wednesday while traveling in a pickup truck from Los Reyes to the indigenous village of Cocucho in the municipality of Charapan, the victims' families said.
The men were on their way to buy a cow to slaughter for the meal to celebrate the feast day of the Virgin of the Nativity.
Federal security forces found two human heads Monday in Antunez, Michoacan.
Police continued 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 gunslinger known as "El Marino" 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 Federal Police on Wednesday arrested a man suspected of disposing of bodies for the Templarios.
Jesus Sanchez Huerta, known as "Chucho the dismemberer," was detained in Apatzingan, the cartel's main stronghold.
Los Caballeros Templarios (Knights Templar), 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.
Civilians began arming themselves a year ago to fight the 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