Mexico has extradited to the US a senior member of the Sinaloa drug gang formerly headed by Joaquin "El Chapo" Guzman.
Damaso Lopez is alleged to have been responsible for organising Guzman's escape from a high security jail in 2001.
He then joined the cartel and became one of the drug lord's closest allies.
He was captured last May and is seen by the US as a key witness in the case against Guzman who is in a US jail.
Damaso Lopez is known as "The Graduate" because he studied law and was a senior official in the Mexican prison administration system.
Arrested last year in Mexico city, he rose in the organisation of the Sinaloa cartel to become one of its leaders.
After Guzman's arrest in 2016, Lopez started a bloody battle with Guzman's sons for control of the cartel.
At the time of his arrest last year he was believed to have been seeking an alliance with Guzman's rival, the Jalisco New Generation Cartel.
Guzman is facing drug trafficking and conspiracy charges.