Months earlier, the U.S. Treasury Department blacklisted more than two dozen people and companies that belonged to what it called a drug-running and money-laundering network that Caro Quintero ran years from behind bars.
A U.S. law enforcement official familiar with the investigation said Caro Quintero, who has not reappeared in public since his release, was passing orders through prison phone calls as well as lawyers and family members who visited him, even as he was shifted between at least three Mexican prisons.
U.S. investigations found a number of upper-tier traffickers have been similarly able to run cartels from behind bars.
"Even without telephone communications you can transmit a lot of instructions that then are followed," said the U.S. official, who agreed to discuss the matter only on condition of anonymity because he wasn't authorized to speak publicly.
David Weinstein, a former assistant U.S. attorney in Miami, said the biggest concern in keeping Guzman in a Mexican prison will be his ability to continue running his global drug empire.
"It could be argued that he would be doing the same thing from a jail, and just bide his time," said Weinstein who previously ran the narcotics section in Miami.
Mexico arrested another of the country's most-wanted men, Zetas cartel head Miguel Angel Trevino Morales, in July, but members of his organization continue to carry out murders, extortion, rapes, robberies and extensive thefts from Mexico's state-run oil company across a wide swath of eastern Mexico, said George Grayson, an expert on the cartel at College of William & Mary in Virginia.
"The sadistic violence continues, and the theft of explosives and chemicals continues," he said.
Keeping hold of Guzman appears to have become a point of national pride Mexico.
"We think he's being perfectly guarded and watched, and we don't think it's necessary to do anything else," Interior Minister Miguel Angel Osorio Chong, the country's highest law-enforcement official, told The Associated Press. "He will be very isolated. He won't be allowed to continue with his operations."
Associated Press writers Katherine Corcoran and E. Eduardo Castillo in Mexico City and Alicia A. Caldwell in Washington contributed to this report.
Michael Weissenstein on Twitter: https://twitter.com/mweissenstein