Mexico has extradited to the United States a "key witness" against imprisoned drug kingpin Joaquin "El Chapo" Guzman, the deputy attorney general said on Friday.
Mexican Guzman has been held in solitary confinement in the US since he was extradited there by Mexican authorities in January 2017.
He is waiting to stand trial in New York in September, accused of running the Sinaloa crime syndicate, one of the world's biggest drug trade empires.
Damaso Lopez, known as "The Lawyer" and once Guzman's right-hand man, "was handed over in Juarez, Chihuahua" in the country's north, deputy attorney general Alberto Elias said in a message to the press.
"Potentially a key witness" against Guzman, the 52-year-old will be tried in a court in Virginia for "criminal association and crimes against health," added Elias.
The message was accompanied by a video of Lopez wearing a hood in a hangar while escorted by police and soldiers. A photo showed him handcuffed in prison uniform aboard an airplane.
Lopez, who bid to take over the Sinaloa cartel leadership after Guzman's capture, was himself caught in a spectacular army-led operation in Mexico City in May 2017.
His capture sparked a wave of armed conflicts and murders in Sinaloa, in the northeast, as a bloody power-struggle raged over the drug cartel's throne.
Lopez had been the deputy director of the Puente Grande prison in the country's west in 2001 when Guzman was held there.
According to the United States Treasury Department, Lopez rose to the rank of a prominent Sinaloa cartel lieutenant after helping Guzman in his first escape from a maximum security prison.
The two have a strong bond: according to some reports, Guzman is the godfather of Lopez's son, who had formed an armed wing of the Sinaloa cartel but crossed the border and turned himself in to US authorities a year ago.
Having remained on the run for 13 years, Guzman, whose nickname means "shorty" in English, was caught in 2014 before escaping again a year later.
He was caught in 2016 and extradited to the US the next year.