The bound and gagged bodies of 26 young men were found dumped Thursday in the heart of Mexico's second-largest city, in what experts said could mark a new stage in the full-scale war between the country's two main drug cartels, Sinaloa and the Zetas.
The bodies were stuffed in two vans and a pickup truck abandoned on an expressway near the Milennium Arches in Guadalajara, one of the most recognizable landmarks in the picturesque city that hosted last month's Pan American Games.
Most of the men died of asphyxia, according to officials in Jalisco state where Guadalajara is located, though initial reports indicated some had been shot.
The victims, apparently between the ages of 25 and 35, all had the words "Milenio Zetas" or "Milenium" written on their chests in oil, said Jalisco state Interior Secretary Fernando Guzman Perez. A law enforcement official who was not authorized to speak on the record said the writing was apparently meant as the killers' calling card, identifying the assassins as being from the Zetas and a smaller, allied gang, the Milenio Cartel.
The official said a banner found in one of the vehicles _ whose contents Guzman Perez refused to reveal _ was in fact signed by the Zetas. Mexican cartels frequently leave threatening messages with the bodies of their victims as a way of intimidating rivals and claiming responsibility for their actions.
The killings, apparently carried out before dawn, bore an eerie similarity to the Sept. 20 dumping of 35 bodies on an expressway in the Gulf coast city of Veracruz.
The victims in the Veracruz mass slaying were purportedly Zetas and the killers were allegedly linked to the Sinaloa cartel; those two cartels have emerged as Mexico's most powerful, and have each been trying to expand into each others' territories.
Raul Benitez, a professor at Mexico's National Autonomous University who studies security issues, said the Guadalajara mass killing may have been retaliation for the Veracruz slayings.
"I think the Zetas are responding by giving back in kind ... it is a game of one-upmanship," said Benitez.
The Guadalajara International Book Fair, which opens Saturday, is expected to draw as many as 600,000 visitors from around the world and describes itself as the world's most important Spanish-language book fair. The bodies were found about a mile (1.6 kilometers) from the Expo Guadalajara events center.
Best known as the home of mariachi music and tequila, Guadalajara also sits on the main highway running through western Mexico from the methamphetamine-producing state of Michoacan north toward the Pacific Coast state of Sinaloa.
In recent months, security officials and analysts have worried that the city could become a target for the Zetas, which has rapidly expanded since breaking with its old allies in the Gulf cartel in 2010.
The Zetas have been expanding west, from their base on the Gulf coast, and Sinaloa has apparently been sending proxy forces eastward into the territory of the Zetas or their allies, in what now appears to have become a nationwide battle.
"As long as there is definition on the division of territories, between Sinaloa and the Zetas, we are going to continue seeing this," said Benitez.
Guadalajara's mayor, Jorge Aristoteles Sandoval, told reporters that "these acts of barbarism show how the war between cartels, and crime, is getting more brutal."
"It's sad to see what's going on," taxi driver Jesus Amado said. "We used to be looking at the problem from afar. Now we're not, we've got it right here."
Officials initially reported that there were 23 bodies found. Ulises Enrique Camacho, a spokesman for the attorney-general's office, said Thursday afternoon that the toll had risen to 26.
Crime in this colonial city of some 1.5 million people was historically dominated by the powerful Sinaloa cartel, but the group's tight grip was shattered by the death of its regional commander, Ignacio "Nacho" Coronel, in a shootout with federal police in July 2010.
Guadalajara's murder rate then soared as factions of the cartel known as the New Generation and the Resistance battled to control Coronel's territory and assets. Street battles have left hundreds dead in the city and surrounding areas.
Killing slowed to a trickle during the Oct. 15-30 Pan American Games, which brought a massive influx of police and soldiers. Law-enforcement officials and analysts said they were nonetheless concerned that a Zetas onslaught could be imminent.
On Wednesday, 17 bodies were found burned in two pickup trucks in a strikingly similar attack in Sinaloa, the home state of the eponymous cartel. Twelve of the bodies were in the back of one truck, some of them handcuffed and wearing bulletproof vests.
Associated Press writers E. Eduardo Castillo and Michael Weissenstein in Mexico City contributed to this report.