Gulf cartel and Guatemalan ex-Kaibiles

"The Gulf and Sinaloa cartels also employ more disciplined groups respectively known as Los Zetas and Los Negros. In July 2006, the Mexican daily Reforma reported findings of a Mexican federal investigation that the Gulf cartel is recruiting MS-13 gang members and Guatemalan Kaibiles. Mexican and U.S. law enforcement officials, however, deny that there are significant ties between Mexican cartels and MS-13(Mara Salvatrucha), indicating that the cartels will work with Central American gangs on specific tasks, but that these gangs are not as disciplined as the cartels, so the cartels have not deepened ties with them."
Direct Source: "Mexico: Gunmen Taking over the Cartels," LatinNews Weekly Report, August 8, 2006; Rolanda Herrera, "Retira PGR a Sicarios," Reforma, August 6, 2006; Rolanda Herrera, "Atribuyen a Movilidad las Capturas de Narcos," El Norte, August 6, 2006; Martín Morita, "Acechan 'Zetas' Sureste," Reforma, July 27, 2006; CRS interview with Mexican Federal Preventative Police (PFP) official, November 14, 2006; CRS interview with FBI officials, January 10, 2007; and, CRS interview with DEA officials, November 8, 2006.
Original source: CRS Report of Congress, Mexico's Drug Cartels, October 16, 2007(CRS means Congressional Research Service Reports), RL34215.
Other Link for..
Mexican Drug War(Wiki en Ingles)
Drug cartel suspected in massacre of 72 migrants, E. EDUARDO CASTILLO, Aug 26, 2010
Guatemalan Army's Kaibliles (official homepage)
Mérida Initiative