May 10, 2012  -- Police found 18 mutilated, headless bodies near a lake popular with tourists and American retirees just outside Guadalajara, Mexico, a massacre that authorities blamed on the Zetas drug cartel.

A phone call alerted police to two vans on a dirt road near Lake Chapala early Wednesday morning. When police opened the van, they found 18 headless and dismembered bodies inside. Some were so badly mutilated that police have still not determined their gender. The bodies appear to have been refrigerated after death.

Handwritten messages were found in the van. "They are clearly messages between rival groups that are in conflict," said Tomas Coronado, prosecutor for the state of Jalisco. Officials said the notes were signed by the Zetas.

PHOTOS of Mexican drug cartel violence.

Los Zetas have been battling the Jalisco New Generation gang, a minor cartel allied with the Sinaloa cartel, which is the Zetas chief rival for dominance of the Mexican drug trade. The Zetas cartel, which was founded by ex-members of the Mexican military, controls most of eastern Mexico and much of the north.

A woman detained yesterday in connection with the separate kidnapping of 12 people in the same area told police that the abductions were connected to events in Tamaulipas state. Two dozen men and women were found decapitated or hanging from bridges in Nuevo Laredo, on the border with Texas, on Friday, where the Zetas are battling the Gulf cartel, another Sinaloa cartel ally.

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