Question: Mario Cárdenas Guillén is the brother of the Mexican drug lord who was the former leader of what group?
Sentence (from "Osiel Cárdenas Guillén"): Originally a mechanic in Matamoros, Tamaulipas, where he was born, he entered the Gulf Cartel by helping Juan García Abrego, the capo at the time; when García Ábrego was arrested in 1996, some infighting erupted within the cartel.
Relevant evidence: No