The Zetas

The Zetas' founders were originally members of the Mexican Army’s elite Grupo Aeromóvil de Fuerzas Especiales (GAFE), trained in locating and apprehending drug cartel members. It is believed that they were originally trained at the military School of the Americas in the United States. Also, they were trained by foreign specialists, including Americans, French, and Israelis, in rapid deployment, aerial assaults, marksmanship, ambushes, small-group tactics, intelligence collection, counter-surveillance techniques, prisoner rescues and sophisticated communications.
In the late 1990s, the drug Gulf Cartel leader Osiel Cardenas Guillen, began to recruit GAFE members to provide protection and perform other vital functions. His top recruit, Lieutenant Arturo Guzmán Decena, brought with him approximately 30 other deserters enticed by salaries substantially higher than those paid by the Mexican government. Guzmán was known as "Z1", and it was after him that Los Zetas was named.
Los Zetas' training locations have been identified as containing the same items and setup as GAFE training facilities, it is also further believed the group employs the same internal organizational structure. Current estimates place Los Zetas around 4000 members strong, which includes several rogue Kaibil members (Guatemalan Army special forces). The name "Zeta" comes from the Federal Preventive Police radio code for high-ranking officers.