The slaughter of at least 20 people in a Monterrey bar is another violent manifestation of the ongoing battle for control of this north Mexico city, a vital link in the drug trade.

As Milenio reports, two trucks full of assault rifle-toting gunmen arrived at the Sabino Gordo bar late Friday night, and opened fire in the crowded establishment. State authorities say that the primary targets in the attack were employees, many of whom hid beneath the tables as the shooting started. As many as 18 of those killed worked at Sabino Gordo.

Because of the location of the attack, speculation about who was responsible centered on the Gulf Cartel and the Zetas, both of whom have a strong presence in Monterrey, the nation’s third-largest city.

However, in a series of public banners, or “narcomantas,” left around the country over the weekend, the Zetas denied responsibility for the crime, attributing it to the Gulf Cartel. Sources inside the Mexico’s federal government told InSight Crime that they suspect agents of the Gulf Cartel fired on the bar because they thought Zetas congregated there.

According to Jorge Domene Zambrano, the security spokesman for the state government in Nuevo Leon, where Monterrey is located, the bar was a center for retail drug distribution. They suspect that retail drug sales were a motivating factor in the attack, and the reason that employees specifically were targeted. They also referred to a man known as Alonso, alias “El Botellero,” as the target, though he was not among the dead. Personal-sized bags of cocaine were found among the wreckage after the shooting.

While the nation’s biggest drug traffickers have traditionally kept retail selling at arm’s length, the growing size of the Mexican market and the fierce competition for territorial control have made it more common for larger groups to get involved.

As one of the nation’s largest and wealthiest cities, Monterrey has one of the most significant retail drug markets in Mexico. Long considered to be among the nation’s safest and best run big cities, the area has been caught in the fallout of the split between the two most powerful criminal groups in Mexico’s northeast: the Zetas and Gulf Cartel. The two groups used to operate as part of the same network, with the Zetas serving as hit men for their Gulf patrons.

However, relations became strained following the 2003 arrest and 2007 extradition of Osiel Cardenas, the Gulf boss who founded the Zetas in the late 1990s, and the two groups began warring openly in early 2010.

As a consequence of the groups’ fighting over control of different cities and trafficking routes, violence has spiked in states where both had a presence, such as Tamaulipas and Nuevo Leon.

Nuevo Leon’s murder rate is not nearly as high as some other Mexican regions — it was less than 20 per 100,000 residents in 2010, and though it is on pace to more than double that figure in 2011, the region is still far less violent than many other Mexican border towns. However, it has risen significant from the range of three to seven murders per 100,000 that had been standard since the 1990s.

Furthermore, the tarnishing of Monterrey, once known as a jewel of northern Mexico, has many worrying about the nation’s ability to handle drug violence. As a recent editorial in the Mexico City daily El Universal said of Monterrey’s troubles:

The second most important city in the country, the central nervous system of our national industry, is at breaking point, on the border between civility and barbarism. If Monterrey falls, as Ciudad Juarez and Reynosa have, the country will be one step away from doing so as well.

While the editorial may overstate the degree of danger in which Monterrey finds itself, the city’s recent decline serves as a stain on Mexico’s reputation and serious challenge for its authorities.

(See El Universal’s video report on the Zeta-Gulf struggle for Monterrey, below).

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