In accepting the Justice Department’s move, U.S. federal judge Carol Bagley Amon said in mid-November that she had no reason to doubt that “Mexican prosecuting authorities sincerely wish to pursue an investigation and prosecution of this defendant.” Cienfuegos was swiftly returned to Mexico.

But he was never imprisoned. And on Thursday night, the Mexican attorney general’s office said he would not be prosecuted.

“After analyzing the evidence sent by U.S. authorities and the material submitted by Gen. Salvador Cienfuegos, the #FGR has concluded that he had no meetings or communications with any criminal group,” the attorney general’s office said in a tweet, using the Spanish-language acronym for the institution. “It has determined it will not take any penal action.”

The case illustrated the power of Mexico’s military, which has become the main force fighting the country’s criminal cartels. Under President Andrés Manuel López Obrador, the armed forces have also assumed a variety of other roles — running ports, delivering vaccines during the coronavirus pandemic, and building airports and other infrastructure projects.

The military has long been subservient to civilian rule, but the government has rarely subjected it to the same congressional oversight or judicial scrutiny as other institutions. Many senior military officials were outraged at the detention of Cienfuegos, whom they viewed as an honest leader. They feared the U.S. arrest might lead to future investigations against other members of the armed forces, according to analysts and officials. Stung by the anger among the military and Mexican politicians, López Obrador threatened to limit anti-drug cooperation with Washington.

Analysts said the quick investigation would do little to resolve doubts about the case.

“Is it possible that Cienfuegos is innocent? Yes. Was there a magnificent opportunity to demonstrate that in an impartial, rigorous and exemplary trial? Yes,” wrote Carlos Bravo Regidor, a well-known analyst and professor at the Center for Research and Teaching in Economics, in a tweet. “Without this trial, is his innocence credible? No.”

U.S. prosecutors said the case against Cienfuegos was strong. But it was built around thousands of BlackBerry messages intercepted in the United States that referred to a shadowy figure called “the Godfather,” who officials said was Cienfuegos. Many Mexicans remained unconvinced. Cienfuegos served as defense minister from 2012 to 2018 under President Enrique Peña Nieto, and was not widely regarded as corrupt.