One witness, Miguel Angel Martínez, told the jurors that Mr. Calderoni provided Mr. Guzmán with secret information on an almost daily basis, including an invaluable tip in the early 1990s that the United States government had built a radar installation on the Yucatán Peninsula to track his drug flights from Colombia.

Mr. Martínez also testified that Mr. Calderoni once informed Mr. Guzmán that the Mexican authorities had discovered a smuggling tunnel he had dug beneath the Arizona border. Before the police could raid the tunnel, Mr. Guzmán was able to make off with a huge supply of cocaine.

But as useful as he was to the kingpin’s operation, Mr. Calderoni met a violent end. In 2003, a gunman approached his silver Mercedes, as it sat parked on a street in McAllen, Tex., and shot him in the head. The authorities have never identified his killer.

Mexico is not the only country to emerge from the trial with its reputation stained. Last month, Juan Carlos Ramírez Abadía, one of Mr. Guzmán’s Colombian suppliers, appeared in Federal District Court in Brooklyn and admitted to having paid off everyone from journalists to tax officials in his country.

A former chief of the North Valley drug cartel, Mr. Ramírez calmly told the jurors that an entire wing of his organization was devoted to doling out payments. “It’s impossible to be the leader of a drug cartel in Colombia without having corruption,” he explained. “They go hand in hand.”

The list of those who took his money was impressive: prison guards, border agents, lawyers and several officers with Colombia’s national police.

Mr. Ramírez boasted from the stand that in 1997, he spent more than $10 million bribing what amounted to the entire Colombian Congress to change the country’s extradition laws in his favor. He also claimed to have paid as much as $500,000 to Ernesto Samper, the former president of Colombia, when he was running for office.