A judge in the western state of Michoacan has begun homicide proceedings against the founder of a vigilante group and 26 of his followers who were involved in a deadly clash with a rival force in December.

Hipolito Mora founded a vigilante force to fight drug traffickers in Michoacan which later become part of an official rural police force that received guns, uniforms and pay from the government. On Dec. 16, Mora's group had a shootout with a rival rural police force led by Luis Antonio Torres, better known as "Simon the American," that left 11 people dead in the remote mountain town of La Ruana, Michoacan.

After the shootout, authorities said Mexican military and federal police would assume security responsibilities in several municipalities, replacing the rural police. In late December, both Mora and Torres, along with 35 of their followers, turned themselves in to authorities.

On Saturday, judge Maria Consuelo Lopez Ramirez said there was sufficient evidence against Mora and his followers of their involvement in 10 homicides during the shootout to merit the launch of proceedings.

Mora's son was killed in the clash, the only death not attributed to his group.

What sparked the shootout at a roadblock was unclear, with each side blaming the other. Authorities have said it stemmed from "animosity and conflicts between self-defense groups."

The vigilante groups emerged in 2013, as farmers and ranchers took up shotguns and hunting rifles to push back against organized gangs exerting control in the region, specifically the Knights Templar cartel.