Vicente Zambada-Niebla, who is thirty-nine years old, is what Mexicans call a “narco junior”—a second-generation drug trafficker. His father, Ismael Zambada, who is known as El Mayo, has long been the No. 2 man in the dominant drug-trafficking organization in the Americas, the Sinaloa Cartel. In 2009, Vicente Zambada was arrested by Mexican authorities and promptly extradited to Chicago, where he was expected to stand trial for importing drugs to that city as a key logistics manager for the cartel.

But then the case took a turn: Zambada’s lawyers declared that he could not be prosecuted by the United States, because, they claimed, he had been secretly working as an informant for the Drug Enforcement Administration, even as he smuggled tons of cocaine across the border. In fact, according to his counsel, Zambada had been assured by his contacts at the D.E.A. that, in exchange for providing them with intelligence about the drug trade in Mexico, he would be guaranteed immunity against prosecution for his own role in the business.

The news of this unorthodox defense strategy, which became public in 2011, contributed to the deepening cynicism on both sides of the border about the war on drugs. A flurry of filings in the federal court in Chicago revealed that Zambada had indeed met in Mexico City with representatives of the D.E.A., to whom he had been introduced by a Sinaloa consigliere-turned-informant. The Department of Justice acknowledged as much, but denied that any quid pro quo had been arranged. In any case, they explained, individual D.E.A. agents are not authorized to hand out irrevocable get-out-of-jail-free cards to men like Zambada. And so, with both sides sticking to their stories, it appeared that the truth would only come out when his case came to trial in 2012.

But the trial was delayed, and delayed, and delayed again. The case was so significant that at one point in 2011 officials expressed concern that Zambada would be assassinated before he could stand trial. As any revelation of the details of the case was postponed, theories proliferated. Earlier this year, the newspaper El Universal released a report, drawing on court documents, which claimed that the D.E.A. had knowingly allowed Zambada to smuggle “billions of dollars” of narcotics into the U.S. The newspaper contended that the conspiracy ran even deeper, alleging that the governments of both the United States and Mexico had, in effect, played favorites among the rival trafficking organizations, secretly colluding with the Sinaloa cartel in order to wipe out its rivals.

The notion of Zambada as a kind of Mexican Whitey Bulger, allowed to operate with impunity in exchange for passing along bits of information about his enemies, has a certain intuitive appeal—and no one could deny that the drug war entails plenty of devil’s bargains. But this particular conspiracy theory always struck me as too neat. For one thing, the D.E.A.’s use of informants in drug cartels is hardly a secret: for drug cops, snitches, along with wiretaps, are the primary tools to attack an organization, not signs of covert collusion. As an analysis of the Zambada case on the Web site InsightCrime puts it: “This is not some conspiracy to protect or favor certain groups—it is a tactic employed by the D.E.A. and other US agencies to allow them to focus efforts on priority targets.”

Still, the long delay in the trial amplified the suspicion that there were explosive secrets just waiting to spill out. Today, the Justice Department revealed that Zambada will not be tried at all, because he pled guilty and agreed to coöperate with the government—more than a year ago. In a secret plea agreement, which was unsealed on Thursday, Zambada confesses that he was a senior figure in the Sinaloa cartel and a “surrogate and logistical coordinator” for his father. He admits to having smuggled “multiple tons” of cocaine, using “private aircraft, submarines and other submersible and semi-submersible vessels, container ships, go-fast boats, fishing vessels, buses, rail cars, tractor-trailers, and automobiles.”

The deal establishes that Zambada will spend at least ten years in prison, with the possibility of a life sentence. But the most intriguing number in the case involves the value of the property and assets that Zambada has agreed to forfeit to the government. Several years ago, Zambada’s father granted a rare interview to the Mexican magazine Proceso. The interviewer mentioned that the head of the Sinaloa cartel, Joaquin (El Chapo) Guzman, had been included on the list of billionaires published by Forbes, and asked whether Zambada had a similar fortune. “That’s just stupid,” the elder Zambada scoffed.

According to the plea agreement, however, the younger Zambada must surrender assets amounting to $1.37 billion—and Zambada did not contest the number. The extent of his property and other holdings in Mexico is unclear, and it would not necessarily be easy for the U.S. government to seize assets held in a foreign country. A D.E.A. spokesman said that Zambada could also possess property in the United States. “We might end up with a Marshals auction,” he said. Among close observers of the Sinaloa cartel, the extent of Chapo Guzman’s own wealth has been a subject of considerable debate. If Zambada’s forfeiture agreement is any indication, perhaps even senior lieutenants in Guzman’s organization merit inclusion on the Forbes list.

If Zambada pled guilty more than a year ago, why are we only finding out about it now? The authorities kept Zambada’s deal under wraps, even as rumors flourished about secret arrangements between the cartel and the D.E.A. The Department of Justice has not disclosed any reasons for the timing of the announcement, but it may have something to do with the arrest, in February, of Chapo Guzman. Within hours of Guzman’s capture in Mexico, U.S. officials announced that they would seek his extradition to face trial in Chicago. That seems unlikely to happen soon, as Guzman must first contend with a series of charges in Mexico. But, if he ever does stand trial in the Windy City, the prosecution will have, in Vicente Zambada, a formidable witness against him.

Above: Vicente Zambada-Niebla in Mexico City in March, 2009. Photograph by Daniel Aguilar/Reuters/Corbis.