Reporting from Nuevo Laredo, Mexico — Residents of this scruffy border town thought they had seen the worst of the violence five years ago, when rival drug gangs staged wild gunfights in the streets and a new police chief was slain just hours after being sworn in.
The warfare gave way to an uneasy calm after one of the warring groups took de facto control. The number of deaths here ebbed, even as violence soared out of control in other border cities, such as Ciudad Juarez, about 500 miles to the northwest.
Now, like a recurring nightmare, dread again hangs over Nuevo Laredo amid a new bloody feud that has ignited widespread fear of a return to the earlier carnage.
Dozens of people have been killed along the border in recent weeks in clashes between northeastern Mexico's most powerful gangs: the Gulf cartel and onetime allies known as the Zetas. Both are based here in Tamaulipas -- a pistol-shaped state that hugs the Texas border and Gulf of Mexico.
Adding to the potential for skyrocketing violence, the Gulf cartel has reportedly reached out for help against the Zetas by enlisting the heavily armed trafficking group headed by Joaquin "El Chapo" Guzman, based in the northwestern state of Sinaloa.
U.S. officials say they have yet to confirm the alliance, but take the reports seriously. Such an alignment would reshuffle Mexico's drug underworld and could produce prolonged and bitter warfare here.
"You'd hate to have that, where Sinaloa does reinforce Gulf or Gulf is able to sustain itself in a way that this conflict between them just keeps going on and on and escalating," said a senior U.S. law enforcement official in Mexico City.
If so, Tamaulipas would be the latest battle zone along the U.S.-Mexico border. In Ciudad Juarez, a turf war between the Sinaloa group and a locally based cartel has left more than 4,000 people dead since early 2008. Last weekend, gunmen in Juarez killed two U.S. citizens -- a consular employee and her husband -- and a Mexican man married to another staff member at the U.S. Consulate there.
Here in Tamaulipas, friction between the Gulf group and the ultra-violent Zetas, which once served as its armed wing, erupted into open fighting after a Zeta leader, Victor Perez Mendoza, was slain in the border city of Reynosa in January, apparently by a member of the Gulf group.
