All the 29 drug cartel figures sent to the US on Thursday were brought from prisons across Mexico to board planes at an airport north of Mexico City that took them to eight US cities.

Alleged drug cartel boss Rafael Caro Quintero, who spent decades in prison in Mexico for the murder of a U.S. drug enforcement agent, pleaded not guilty in a U.S. court on Friday to drug trafficking charges that could result in his execution.

Rafael Caro Quintero, nicknamed “El Narco de Narcos” (The Narco of Narcos) is the founder of the now defunct Guadalajara Cartel—one of the most powerful drug cartels of the 1980s that later splintered into various groups, including the Sinaloa Cartel, one of the world’s most powerful criminal organizations and drug cartels.