Prosecutors say a former Mexican cartel leader could spend the rest of his life in a U.S. prison after pleading guilty to drug and assault counts in South Texas.

Jorge Costilla Sanchez pleaded guilty Tuesday to conspiracy to possess with intent to distribute cocaine and marijuana, plus two counts of assault on a federal officer. The 46-year-old Costilla remains in custody pending sentencing in Brownsville.

Prosecutors say Costilla led the notorious Gulf Cartel. He was arrested in 2012 in Mexico and extradited to the U.S. in 2015.

The assault charges arose from a 1999 incident in which two U.S. agents, assigned to the U.S. consulate in Monterrey, Mexico, were followed in Matamoros, Mexico. Prosecutors say cartel members threatened to kill the U.S. agents, who persuaded the gunmen to free them.