The Zetas, once the military wing of the Gulf Cartel, are now among one of the most violent groups in Mexico, with a growing presence in neighboring Guatemala. The Zetas started out as an enforcer gang for the Gulf Cartel, taking their name from the radio code used for top-level officers in the Mexican army. Not only are they highly organized, but their use of brutality and shock tactics -- petrol bombs, beheadings, and roadblocks -- has led the United States Drug Enforcement Administration (DEA) to describe them as perhaps “the most technologically advanced, sophisticated and violent of these paramilitary enforcement groups."