Police in Guerrero state, Mexico, collaborated with a drug cartel to kill a group of student protesters, according to the state attorney general, highlighting the often blurred line between criminals and law enforcement across the country.

Guerrero Attorney General Iñaky Blanco said that police in the city of Iguala had handed 17 student protesters to the Guerreros Unidos -- a splinter group of the Beltran Leyva Organization -- reported Animal Politico. Two members of the group confessed to killing the students, and said that 30 officers in Iguala's municipal police were members of their cartel, according to the official.

The protest took place in the city of Iguala on September 26, with students from a local teacher's college protesting job discrimination against teachers from rural areas. Police opened fire on buses transporting the protesters, killing six, then reportedly herded a large group of students into police vehicles and drove away. Forty-three students are still missing.

Blanco also announced that 28 bodies had been found in mass graves close to the city, in the same area where the two detainees said they had killed the students. The authorities haven't yet identified the bodies, due to their state of decomposition.

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If the attorney general's statement is accurate, the case underscores the often close relationship between state and criminal actors in the region. An arrest warrant has been issued for Iguala's mayor, who is accused of taking part in the violence, while the city's police chief is also under investigation. 

The Guerreros Unidos formed as a breakaway faction of the Beltran Leyva Organization (BLO), following the death of Arturo Beltran Leyva in 2009. The group is engaged in a bitter turf war with Los Rojos -- another splinter cell of the BLO -- and the Knights Templar for control of Guerrero's drug trafficking routes.

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The case of the student disappearances also highlights Mexico's dismal record on human rights, coming soon after claims that the army executed 22 suspected criminals. Amnesty International has reported (pdf) that criminal groups often collaborated with public officials to commit extrajudicial killings under the administration of former President Felipe Calderon, during which over 26,000 people were reported missing.