United States authorities have not been able to trace the fortune of drug lord Joaquín Guzmán, better known as “El Chapo”, according to Mexico’s attorney general. He is believed to have made at least $1 billion in illicit earnings from his Sinaloa drug cartel, according to The Guardian.

“As of today, US authorities have not found even one dollar of El Chapo’s assets,” Raul Cervantes said in a TV interview on Wednesday. “His money hasn’t been found because he didn’t use the financial system.” Cervantes made the statement during an interview about the arrest of Guzmán’s former aide Dámaso López on Tuesday.

Guzmán was captured in January 2016. He is facing a number of charges in a New York court. On January 21, he had pleaded not guilty to 17 federal charges against him, including running a criminal organisation, conspiring to murder his rivals, money laundering and firearms violations.

Prosecutors have not sough the death penalty against Guzmán as part of the extradition conditions set by the Mexican government. Instead, they have sought life imprisonment and the forfeiture of his assets.

Guzmán was first indicted by US courts in the 1990s. The 59-year-old smuggler’s career began in opium and cannabis-farming and expanded to include what is believed to be the largest transnational cocaine, heroin and methamphetamine smuggling operation with a presence in Europe and Asia. He managed to escape twice from Mexican prisons during his incarceration and reportedly controlled operations from his cell.