By Will Grant
BBC Mexico correspondent
Publishedduration50 minutes agoimage copyrightReutersimage captionThe ex-defence chief was arrested at Los Angeles airport last month
In unsealed court documents in October, US prosecutors claimed former Mexican Defence Minister Salvador Cienfuegos Zepeda was also known as "the Godfather".
His mafia-don pseudonym reflected his alleged standing at the top of a pyramid, the prosecutors argued, which incorporated the armed forces, the Mexican government and the "extremely violent" H-2 drug cartel.
General Cienfuegos was accused of using his high-ranking position to provide the cartel with unique protection by tipping them off to military operations against them and directing the army and its resources against their rivals.
He was also accused of more prosaic drug-trafficking crimes, such as receiving multi-million-dollar bribes and smuggling heroin, cocaine, methamphetamine and marijuana into the US.
The charge sheet – which he denied – was explosive. Gen Cienfuegos was the highest-ranking Mexican official ever to be arrested on drug-trafficking charges. But this was no joint US-Mexico operation or shared investigation involving agents on both sides of the border.
Rather, officials at the US Drug Enforcement Administration (DEA) were so wary of word getting back to their target that the first anyone in the Mexican government heard of the case him was when the 72-year-old former general was detained on his arrival in Los Angeles with his family.
Yet now – to employ the "big-fish" metaphor for drug cartels – those same officials at the DEA and the Department of Justice have just let what was supposedly the biggest catch of their careers back into the water.
As they asked a federal judge in New York to dismiss the charges against Gen Cienfuegos, US prosecutors cited "sensitive and important foreign policy considerations" which they said "outweighed" the government's interest in pursuing the prosecution.
The judge, Carol Bagley Amon, noted that there was an element of "a bird in the hand" in having such a notable figure on such serious charges in her court, but ultimately concluded that she had no reason to doubt the "sincerity" of the government's decision.
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So, instead of potentially facing a long jail sentence in the US alongside convicted drug lord Joaquin "El Chapo" Guzmán, Gen Cienfuegos returned to Mexico as a free man.