Mexican drug boss Joaquin “El Chapo” Guzman was moved on Saturday from a jail in central Mexico to a prison in Ciudad Juarez, a northern city on the U.S. border, in a move that appears to bring him closer to extradition to the United States.

Guzman, head of the Sinaloa drug cartel, was one of the world’s most wanted drug kingpins until his capture in January, six months after he broke out of a high-security penitentiary in central Mexico through a mile-long tunnel.

Chapo, or “Shorty,” faces charges ranging from money laundering to drug trafficking, kidnapping, and murder in cities that include Chicago, Miami and both Brooklyn and Manhattan, New York.

His lawyer, Juan Pablo Badillo, said Guzman was moved early on Saturday, but he was not sure why.