The six-page report, written by senior associates Adam Isacson and Maureen Meyer, is based on an approximately week-long trip to the Rio Grande Valley and Laredo sectors of the US-Mexico border in November 2011. The authors visited three cities in Texas -- Laredo, McAllen, and Brownsville -- and one city in Mexico, Matamoros. 

Among the report's findings is that US law enforcement authorities say that the Zetas' power in the area is ebbing slightly. The Zetas' traditional stronghold is in three Mexican states that border Texas: Coahuila, Nuevo Leon, and Tamaulipas. The report states that part of the group's decline is due to internal divisions, an apparent reference to factions that have reportedly turned against the group's surviving top leader, Miguel Treviño Morales, alias "Z-40." The report also notes that increased drug seizures along the border may also be a sign that the Zetas' control over drug smuggling routes has been weakened, and that "different groups" may now be attempting to move drug shipments into the US via these routes. 

These increased drug seizures are one indication that drug trafficking has increased in both the Rio Grande Valley and Laredo sectors, with US agents noting increased seizures of heroin, marijuana, and a new substance: liquid methamphetamine. 

While the continued weakening of the Zetas would likely lead to increased violence in this region, should a power vacuum in the criminal underworld emerge, so far there is no sign of any "spillover" violence in the US, the report adds. 

InSight Crime Analysis 

One reason for the Zetas' weakening hold in this region of the US-Mexico border is likely the group's drawn-out war with the Sinaloa Cartel. The two organizations are fighting for control of Nuevo Laredo, which as WOLA points out is the busiest land port in the US, with some 7,000 trucks crossing daily in and out of Mexico. This commercial activity has made the "plaza" extremely valuable to drug trafficking organizations. Not only are the Zetas fighting the Sinaloans in Laredo, they are also clashing in the central state of Durango. This conflict, along with the aftermath of the death of Zetas leader Heriberto Lazcano, alias "Z-3," in October, has put the Zetas in a much more vulnerable position.

The WOLA report also raises the question of how the Zetas' decline in this border region will affect migration dynamics. The Zetas are known for charging a tax, or a "piso," on smugglers who move migrants through their territory, killing, kidnapping and even forcibly recruiting the migrants who do not pay up. The WOLA report notes that greater numbers of Central American migrants are attempting to move through Zetas' territory, the Mexican state of Tamaulipas, into the Rio Grande Valley in the US. While Tamaulipas has witnessed brutal acts of violence against migrants, including the slaughter of 72 migrants in August 2010, the state remains a popular crossing point as it is the shortest distance between the US-Mexico border and Central America. 

As dangerous as the Zetas made Tamaulipas for migrants, it's possible that the Zetas' decline could make migrants even more vulnerable. As InSight Crime previously documented in a three-part report on the dangers facing migrants, the Zetas are not the only organization who pose a threat to those moving northwards from Central America. The Zetas typically contract street gangs to harass, rob, and even kidnap migrants as they move along their route. With the Zetas weakening, this could possibly empower street gangs to prey on migrants even more aggressively, in order to keep the money extorted from migrants for themselves. If the Zetas continue to lose power and influence along the US-Mexico border, it will likely make migrants' journey even more dangerous and unpredictable.