The claim was made by attorneys in defense of Mexico's Vicente Zambada-Niebla, who was extradited to the United States to face drug-trafficking charges in Chicago, the El Paso (Texas) Times reported.
If the claim is true, it could prove to be as damaging to federal investigators as the Alcohol, Tobacco and Firearm's "Operation Fast and Furious," that let U.S. weapons get into Mexico, the report said.
Documents filed in U.S. federal court said the Sinaloa cartel was allowed to bring tons of cocaine into the United States in exchange for information about rival cartels, The Houston Chronicle reported.
The documents also said Zambada-Niebla worked as an informant for the U.S. government while he was a known fugitive.
Zambada-Niebla's legal team wants a U.S. judge to drop charges against their client because his alleged agreement with the government reportedly promised him immunity from prosecution.
Federal prosecutors and the U.S. Drug Enforcement Agency declined to comment on the case.
Zambada's lawyers said as recently as 2008 his client and a top cartel lawyer allegedly met at a Mexico City hotel with two DEA agents, where he was reportedly promised immunity.
In "Fast and Furious," the ATF botched a sting to catch weapons traffickers by allowing a load of illegally purchased guns slip into Mexico. The shipment was lost and some of the guns turned up at crime scenes, including one where a U.S. Border Patrol agent was killed.
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