Police described Manuel Alvarez as "the main operator of money laundering" in one of Mexico's largest criminal organizations, the Sinaloa cartel, which has been led for decades by Guzmán, who is also known as "El Chapo."
Guzmán, who was first arrested in the early 1990s, has twice absconded from Mexican prisons in spectacular fashion.
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After tunneling out of a maximum security facility last July, he was caught earlier this year — but only after giving an interview to actor Sean Penn, who wrote a lengthy story about the encounter for Rolling Stone. (The Mexican actress Kate Del Castillo, who helped arrange the meeting, has questioned parts of Penn's account.)
Shortly after Guzmán's capture in January, Mexican authorities began the process of extraditing him to the United States, where the federal government in at least five jurisdictions is vying to prosecute him on drug trafficking charges.