كارتل
Reports vary as to who triggered the formal split and why. Some sources claim that Guillén, brother of Cárdenas and one of the successors of the Gulf Cartel, was addicted to gambling, sex, and drugs, leading Los Zetas to perceive his leadership as a threat to the organization. Other reports mention, however, that the divide occurred due to a disagreement on who would take on the leadership of the cartel after the extradition of Cárdenas. The candidates from the Cartel were Guillén and Jorge Eduardo Costilla Sánchez, while Los Zetas wanted to hand the leadership to their own head, Lazcano. The Cartel also reportedly began looking to form a truce with the rival Sinaloa Cartel, which Los Zetas did not want to recognize, allegedly preferring an alliance with the Beltrán-Leyva Cartel. Samuel Flores Borrego, a lieutenant of the Cartel, killed Zetas lieutenant Sergio Peña Mendoza, alias "El Concorde 3", due to a disagreement over the drug corridor of Reynosa, whom both protected. Los Zetas demanded that the Cartel hand over the killer, but they refused.