A Mexican drug lord notorious for his role in a U.S. drug enforcement agent’s brutal 1985 murder was arraigned on sweeping drug-trafficking charges in New York on Friday.

The arraignment of the drug lord, Rafael Caro Quintero, a founding member of the Sinaloa Cartel, came a day after he was transferred to the United States from Mexico in a move that potentially signaled a new era of cooperation between the two countries.

Mr. Caro Quintero was arraigned in Federal District Court in Brooklyn along with Vicente Carrillo Fuentes, a former leader of the Juarez Cartel.

Mr. Caro Quintero, 72, was charged in a superseding indictment in 2020 with smuggling thousands of kilograms of illegal drugs across the U.S. border as well as with a four-decade effort to murder his rivals. Mr. Carrillo Fuentes, 62, was charged in a separate indictment with similar crimes from 1990 to 2014.

The arraignments came a day after the Mexican authorities turned the two men and 27 other top drug-cartel operatives over to their American counterparts in an extraordinary move. The transfer was widely seen as a sign of Mexico’s willingness to increase its cooperation with U.S. plans to crack down on its criminal mafias.

President Trump and his allies have pressured Mexico’s president, Claudia Sheinbaum, with threats of tariffs on her country’s goods and suggestions that the United States might take military action in Mexico if officials there did not work to stem the flow of drugs.