Updated

After months of tacit cooperation with rural vigilantes trying to drive out a vicious drug cartel, the Mexican government has moved to solve one of its toughest security problems with a plan to legalize the growing movement and bring it under the army's control.

The risks are high.

To succeed, the government must enforce military discipline and instill respect for human rights and due process among more than 20,000 heavily armed civilians before sending them back home to the western state of Michoacan.

In other Latin America countries, similar experiments have created state-backed militias that carried out massive human rights abuses as armed civilians turned to vengeance, or assisted in mass killings. The Mexican army itself is accused of abuses in the drug war.