The slippery co-founder of the Sinaloa drug cartel, whose notorious kingpin Joaquin “El Chapo” Guzman Loera is serving a life sentence in Colorado, is now in U.S. custody, officials said Thursday.For years, Ismael "El Mayo" Zambada Garcia, 76, evaded authorities in Mexico, where he ran the white-collar side of the cartel. The State Department had offered a $15 million reward for his capture.Also Thursday, one of El Chapo's sons, Joaquin Guzman Lopez, was taken into custody in El Paso, Texas, along with El Mayo, U.S. Attorney General Merrick Garland said in a statement.Last year, another son of El Chapo, Ovidio Guzman Lopez, was extradited to Chicago to face drug conspiracy charges. Joaquin Guzman Lopez is charged in the same case, along with two other sons of El Chapo who remain at large.It was unclear where in the United States that El Mayo will be taken for his initial court appearance. Joaquin Guzman Lopez is expected to join his brother in Chicago in the case here.Both men are facing multiple charges in the United States for leading the Sinaloa cartel’s criminal operations, including its deadly fentanyl manufacturing and trafficking networks."Fentanyl is the deadliest drug threat our country has ever faced, and the Justice Department will not rest until every single cartel leader, member, and associate responsible for poisoning our communities is held accountable," Garland said Thursday. Related Group tied to El Chapo’s sons reportedly orders halt to manufacture of fentanyl in Mexico, but experts are skeptical In 2013, El Mayo's son, Vicente Zambada-Niebla, was extradited to Chicago in a sweeping 2009 indictment of El Chapo, El Mayo and their lieutenants.Six years later, in 2019, Zambada-Niebla, a logistics guru for the cartel, was sentenced to 15 years in prison under heavy security at the Dirksen federal courthouse in Chicago. The same year, he testified against El Chapo in New York, where he talked about his father’s role in the operation.He testified that his father’s bribery budget was often as much as $1 million per month, with bribes going to many high-level Mexican public officials.Zambada-Niebla, known as Mayito, had coordinated trains, ships, submarines and even a Boeing 747 as he moved cocaine and heroin to the United States for the cartel, prosecutors said.In a call arranged by federal authorities after Zambada-Niebla's arrest, his father, El Mayo, gave his son the go-ahead to cooperate with U.S. authorities against Sinaloa leaders, according to law-enforcement sources involved in the Chicago investigation of the cartel.In February, federal authorities in Brooklyn had charged El Mayo with conspiracy to manufacture fentanyl, a powerful drug that’s left thousands dead in Chicago. El Mayo also faces charges in the original federal case against the Sinaloa cartel, filed in Chicago in 2009.The circumstances of El Mayo’s arrest were unclear. According to news reports, he'd arranged his detention with U.S. officials and was arrested Thursday afternoon at a private airport in El Paso.“I know this has been in the works for some time,” said Jack Riley, a former deputy administrator of the U.S. Drug Enforcement Administration during the Obama administration who previously ran the DEA’s office in Chicago.“I would not be surprised at all if Chapo and his family had something to do with it," he said. "Mayo is an aging bad guy that I believe was feeling heat from his younger rivals and wanted to attempt to cut a deal like his son.”According to the DEA, in a statement in February when El Mayo was charged in the fentanyl case, he “employed individuals to obtain transportation routes and warehouses to import and store narcotics and ‘sicarios,’ or hit men, to carry out kidnappings and murders in Mexico to retaliate against rivals who threatened the cartel. The millions of dollars generated from the drug sales were then transported back to Mexico.” Related How a West Side drug bust led the feds to ‘El Chapo’ They were 2 Chicago pizza delivery guys. Then, they ran a Mexican drug cartel, feds say