One morning earlier this summer, on a dirt road outside the border city of Nuevo Laredo, Mexican authorities stopped a pickup truck carrying Miguel Angel Treviño Morales, the legendarily sadistic leader of Los Zetas, an ultraviolent criminal organization that has become one of the dominant players in Mexico’s drug trade. The origin story of the Zetas is telling: the first members were defectors from Mexico’s élite special forces, who traded allegiances in the drug war and went into business with the cartels. With the destructive imagination of a serial killer, Treviño Morales, who was known as Z-40, presided over innumerable acts of torture, murder, and dismemberment, and became, in the process, a symbol of the recent reign of terror in Mexico. His capture was celebrated as an indication that Mexico’s new President, Enrique Peña Nieto, who took office last year, might be capable of truly confronting the cartels.

Observers on both sides of the border had wondered about Peña Nieto’s resolve. He came into office promising to adopt a different approach than his predecessor, Felipe Calderón, who had waged war on the cartels—with encouragement and logistical support from the United States which stopped just shy of boots on the ground. Calderón’s strategy secured affection in Washington, where he is still regarded by American drug warriors as a staunch ally in the cause. But, as a policy, his frontal assault was a failure: the flow of drugs across the border did not diminish to any meaningful extent, and the two dominant trafficking organizations—the Sinaloa cartel and the Zetas—both made gains in territory and influence during the Calderón years. Many of these groups, especially the Zetas, have branched into migrant smuggling, kidnapping, extortion, and other crimes.

If the benefits of the crackdown were few, the costs were great: no one knows precisely how many Mexicans lost their lives to the drug war during the Calderón years. The number one often hears is sixty thousand.

So it made sense that Peña Nieto would seek a different approach. What that might entail, though, was always a little vague. He said that he would focus on public safety and on bringing down the number of homicides, but not how he would go about it. Some worried that he might simply leave the cartels alone, figuring, not unreasonably, that most of the narcotics that move through Mexico are consumed by Americans. Peña Nieto’s political party, the Partido Revolucionario Institucional (PRI), held power in Mexico for seven decades prior to 2000, and the hands-off strategy (underwritten, generously, by bribes from the cartels) was a feature of its tenure. A détente with the drug lords seemed all the more likely when Peña Nieto assumed a more arm’s-length relationship with American officials from the Drug Enforcement Administration and other agencies that had worked so intimately with his predecessor. If Calderón stood accused of having confused his own country’s interests in the drug war with those of his allies, the new President seemed eager to reassert Mexico’s autonomy.

In light of this pivot, the capture of Treviño Morales suggested a resolve on the part of Peña Nieto that many suspected he did not possess. There have been several significant arrests since: last month, the Gulf Cartel leader Mario Ramírez Treviño was captured. Last week, a notorious Sinaloa lieutenant known as El Mayito, who is suspected of playing a role in three hundred and fifty murders, was arrested in Juárez.

But these high-profile captures have been offset by a significant release: on August 9th, a silver-haired trafficker named Rafael Caro Quintero was quietly let out of prison. Caro Quintero had masterminded the kidnapping and murder of a D.E.A. agent, Enrique (Kiki) Camarena, in 1985. In American law-enforcement circles, Camarena is a famous martyr of the drug war. His life and death were chronicled in a book and his photo is still prominently displayed in many D.E.A. facilities. Caro Quintero, who was twenty-eight years into a forty-year sentence, was being held at Puente Grande, the ostensibly maximum-security prison in Jalisco from which Mexico’s most famous drug trafficker, Joaquín (El Chapo) Guzmán Loera, escaped, in 2001. He was set free on a technicality, and walked out of the prison at 2 A.M.—an hour that says a lot about the transparency and the accountability of that decision. As soon as U.S. officials learned of the release, they demanded that Mexico rearrest Caro Quintero. But by that time he had disappeared.

The release of Caro Quintero demonstrates that Mexico’s institutions of criminal justice—not just its prisons but its judges—are too eroded by corruption to make a credible case for their own autonomy in administering justice for Treviño Morales. Peña Nieto should be applauded for his success in effecting the capture of the head of the Zetas, but if Z-40 is to be held accountable for his long résumé of murder and destruction the only responsible thing for Peña Nieto to do is to extradite him to the United States.

In the language of drug and alcohol addiction, some relationships are described as “enabling,” and in the intimate rapport between the United States and Mexico the dysfunction operates both ways. Mexico is the biggest exporter of narcotics on the planet, because its neighbor to the north is the biggest importer. Mexico’s cartels enable our addictions; our prolific consumption of drugs enables corruption and bloodshed in Mexico.

Peña Nieto has many reasons for wanting to reëvaluate his country’s posture in the drug war—and its codependency with the United States. For one thing, the U.S. is in the process of legalizing a narcotic whose prohibition we still ask our friends in Mexico to lay down their lives to defend. There is no question that the worst consequences of the Zetas’ misdeeds have been endured by the Mexican people. But the criminal organizations have accumulated such power, and wrought such carnage, that it would be folly for Peña Nieto to seek an accommodation with the cartels, or to adopt the old PRI posture of well-compensated neglect. To be sure, the capture of Z-40 is a promising sign. But the real test of Peña Nieto’s resolve will be whether he is prepared to sacrifice Mexico’s autonomy in the interests of justice—and send the most feared criminal in his country’s history to face trial in the United States.

Photograph: Susana Gonzalez/Bloomberg/Getty