The Zetas -- headquartered in Nuevo Laredo, Mexico, directly across the border from Laredo, Texas -- make up Mexico's largest drug cartel in terms of territory. The group has operations in 11 Mexican states.

Another reputed Zetas leader, Ivan Velazquez Caballero, alias "El Taliban," was captured last month.

Lazcano, 37, joined the Mexican armed forces in 1991 and was part of its elite airborne special forces group, dedicated to battling drug cartels.

Soon after, Lazcano and several other special forces members were recruited by the Gulf cartel to create its enforcement arm, Los Zetas.

In ensuing years, the Zetas split into a major drug trafficking organization and have since branched out into extortion, kidnapping and human smuggling.

The cartel is in the midst of a bloody turf war with its former employer, the Gulf cartel, and also with the Sinaloa cartel. The fight for access to lucrative smuggling routes in northern and central Mexico has left thousands of civilians dead.

The violence is particularly acute in three northeastern states that are some of the Zetas' strongest-held territory: Coahuila, Nuevo Leon and Tamaulipas.

In 2010, the bodies of 72 migrants from Central and South America were discovered at a ranch in Tamaulipas state. The Zetas have been blamed for the mass graves and for the deaths of the migrants.

The cartel also is blamed for setting a fire at a casino in Monterrey that killed 52 people.

In May, authorities found 49 decapitated and dismembered bodies along a highway in Nuevo Leon. The orders to commit the grisly crime allegedly came from Lazcano, who originally wanted the bodies to be left in a town's central square. In banners purportedly hung by the cartel, the group denied involvement.

Mexican officials have said that more than 47,500 people have been killed in drug-related violence since Calderon began his crackdown on cartels in December 2006. Some groups say the number is much higher.