Gulf Cartel, which lost much of its influence after it separated from Los Zetas in early 2010. Mario took the leadership of the Gulf Cartel after the death of his brother Antonio Cárdenas Guillén, alias Tony Tormenta, in November 2010. Nonetheless, the death of his brother, among other things, created a division in the Gulf Cartel: those loyal to Cárdenas Guillén and those loyal to Jorge Eduardo Costilla Sánchez. The latter, however, reportedly enjoys some protection from the Mexican military and aid of the Sinaloa Cartel, another drug trafficking organization. Nonetheless, the arrest of Mario weakens the power of the Cárdenas Guillén family. A close associate of Mario known as Juan Gabriel "Sierra" Montes was captured by the Mexican Naval Infantry in Guadalajara, Jalisco on 11 September 2012. He allegedly conducted drug trafficking operations for the Gulf Cartel and headed a hit squad faction in the cartel called Los Kalimanes. Gulf Cartel infighting Background In the late 1990s, Osiel Cárdenas Guillén, the former leader of the Gulf cartel, had other similar groups besides Los Zetas established in several cities in Tamaulipas. Each of these groups were identified by their radio codes: the Rojos were based in Reynosa; the Metros were headquartered in Matamoros; and the Lobos were established in Laredo. The infighting between the Metros and the Rojos of the Gulf cartel began in 2010, when Juan Mejía González, nicknamed El R-1, was overlooked as the candidate of the regional boss of Reynosa and was sent to La Frontera Chica, an area that encompasses Miguel Alemán, Camargo and Ciudad Mier – directly across the U.S.–Mexico border from Starr County, Texas. The area that Mejía González wanted was given to Flores Borrego, suggesting that the Metros were above the Rojos. Unconfirmed information released by The Monitor indicated that two leaders of the Rojos, Mejía González and Rafael Cárdenas Vela, teamed up to kill Flores Borrego. Cárdenas Vela had held a grudge on Flores Borrego and the Metros because he believed that they had led the Mexican military to track down and kill his uncle Antonio Cárdenas Guillén (Tony Tormenta) on 5 November 2010. Other sources indicate that the infighting could have been caused by the suspicions that the Rojos were "too soft" on the Gulf cartel's bitter enemy, Los Zetas. When the Gulf cartel and Los Zetas split in early 2010, some members of the Rojos stayed with the Gulf cartel,