MEXICO CITY (AP) — A man believed to be the leader of the Gulf drug cartel, which controls some of the most valuable and violently contested smuggling routes along the U.S. border, was arrested by Mexican marines and presented to the public Thursday morning.

The capture of Jorge Eduardo Costilla Sanchez is a major victory in the military battle against drug trafficking, but it could open a power vacuum and intensify a struggle south of the Texas border in northeast Mexico, a region that has seen some of the most horrific violence in the country’s six-year war among law-enforcement and rival gangs.