In 2006, a Texan named Edgar Valdez Villarreal was at an inflection point in his drug-smuggling career. Valdez was thirty-three and known as La Barbie for his blond hair and blue eyes, the fair-skinned look that Mexicans call güero. A former high-school linebacker from Laredo, he had spent about fifteen years shipping marijuana, and later, cocaine, to Georgia, Louisiana, Mississippi, and Tennessee. During the late nineteen-nineties, he was one of many smugglers operating across the border, in Nuevo Laredo, the largest inland port in Mexico. The drug trade had been relatively peaceful. Each smuggler paid sixty thousand dollars a month to the local plaza boss, a man named Dionisio García, known as El Chacho, who in turn paid the bribes that insured the trafficking routes.

But in 2000, the Gulf cartel began to take over Nuevo Laredo, and gave every crook in town an option: join or die. El Chacho was killed, and La Barbie fled to Acapulco. He joined a clan from western Mexico, the Beltrán-Leyva brothers, who were associates of the powerful Sinaloa cartel, led by Joaquín Guzmán Loera, known as El Chapo. La Barbie prospered with the Beltrán Leyva cartel, a group of four brothers led by Arturo Beltrán Leyva, known to authorities as A.B.L. Government sources say the group imported about forty tons of coke per month through the southern port at Zihuatanejo. La Barbie, together with the Beltrán Leyvas and the Sinaloans, warred against the Gulf cartel for control of Nuevo Laredo. La Barbie orchestrated a bold public-relations campaign on behalf of his crew: he placed newspaper ads and editorials denouncing their rivals, and was supposedly responsible for making a viral video documenting the execution of four assassins who’d been sent to Acapulco to kill him. Soon, he acquired a global reputation as a top player. But by 2006, as the new Mexican President, Felipe Calderón, promised an assault on drug cartels, it became clear that La Barbie’s side had lost.

La Barbie scrambled. He separated from his first wife and married Priscilla, the teen-age daughter of a drug-smuggling associate. He was losing friends and money. Through his attorney, he contacted the Drug Enforcement Administration in Laredo, which wanted an informant to help capture A.B.L. and El Chapo Guzmán. La Barbie offered to help the D.E.A. get A.B.L. or Guzmán, but not both, and he had several requests; among them, he wanted to bring six million dollars into the United States and get a case against his cousin dropped. The agents he spoke to were eager to strike a deal, but their boss quashed the negotiation. “It got to the point,” a retired D.E.A. agent who was involved in the talks told me, “where management said, ‘He’s a fucking doper; if he doesn’t want to coöperate, screw him.’ ”

Undaunted, La Barbie shopped his intelligence at other federal agencies—the C.I.A., Immigration and Customs Enforcement—and found a receptive ear at the F.B.I., which, coördinating with Mexican law enforcement, used his information to reach A.B.L., who died during a capture attempt in 2009. “At that point, he would’ve loved to come to the States and get a big sentence reduction,” a government official who worked on the case said, of La Barbie. “But there was never an explicit agreement where we told him, ‘Yes, we can help you.’ It was complicated. Too many jurisdictions had charges on him. There’d also been some executions of police officers in Mexico.” La Barbie was controversial, his lawyer at the time, Michael McCrum, told me. “The agents wanted to work with us, but we hit roadblocks from the upper levels of D.O.J. There’d been too much publicity.” He added, “That video didn’t help,” referring to the filmed execution.

When the remaining Beltrán Leyva brothers realized La Barbie had set up A.B.L. with the F.B.I., they marked him for death. He went into hiding, moving around Acapulco, Cuernavaca, and Mexico City. In 2010, he was captured by Mexican federal police. Last month, after five years in prison, La Barbie was extradited to the U.S. in a group that included his father-in-law and eleven other fugitives.

When someone is indicted in a U.S. court and flees to a country with which the U.S. has an extradition treaty, the prosecuting attorney can request extradition. A provisional arrest warrant, known as a PAW, gets the ball rolling: it’s a simple form with the defendant’s name, the issuing court, the agent or investigator, and a factual basis for the charges. The prosecutor sends the PAW to the Office of International Affairs at the Department of Justice, which reviews it, and sends it on to the State Department, which sends it to officials in the country in question—in this case, Mexico’s Ministry of Foreign Affairs, who passes it on to the Attorney General’s Office. They pass it to the appropriate Mexican court. If that court finds probable cause, and the fugitive is arrested or is already in custody, the Americans have sixty days to compile an extradition package, which can include affidavits, fingerprints, witness lists, and coöperating defendants.

Extradition from Mexico is tricky. U.S. prosecutors and defense attorneys said they believe that if a fugitive has a corruption deal with the Mexican government, or simply knows too much about corruption, Mexico may prolong extradition until a new administration is elected, or just prosecute the defendant itself. Another potential tactic: if Mexico lacks charges of its own, the Mexican prosecutor might use the charges from the Americans’ PAW, then later refuse extradition on the basis of “double jeopardy,” the legal principle that prohibits a defendant from being prosecuted twice for the same offense.

Some fugitives actively seek extradition to the U.S., either for safety reasons or because they believe they have valuable information to trade. Hanging over every Mexican extradition is the precedent set by Osiel Cárdenas Guillén, the former Gulf cartel leader. Extradited in 2007 and sentenced in 2010, Cárdenas, who was eligible for a life sentence, is scheduled for release in 2025. His plea agreement remains sealed. But law enforcement sources say that Cárdenas, through his own informant, passed along information about drug loads and the whereabouts of underbosses—the kind of meaningful, real-time intelligence that only a top capo could possess. “Cartel cases often rely on coöperators,” Angel Moreno, a federal prosecutor in Texas, says, of the general nature of these prosecutions. “To many people that coöperator may be the devil, but if he’s going to help us get five other archangels, we’ll probably still use him as a witness.” The worst guys are positioned to make the best deals.

After La Barbie’s arrest, in 2010, Mexican authorities summoned his new lawyer, Kent Schaffer, to discuss an agreement through which La Barbie would be extradited in return for information about several Mexican officials. La Barbie was eager to come home, and confident about his negotiating position. “Shortly before the exchange was supposed to take place, the strangest thing happened,” Schaffer told me. “The government lawyer we were negotiating with, Marisela Morales, suddenly cut off the talks, and said, ‘No deal.’ They went from being gung-ho about extradition to refusing our phone calls.” Schaffer guesses that the Mexican government initially wanted information on officials from the opposing political party, the Institutional Revolutionary Party (PRI), but then worried about collateral damage to their own party, the National Action Party (PAN). Months later, Morales was appointed the first female attorney general in Mexico’s history. (She couldn’t be reached for comment.) La Barbie was left in his Mexican prison cell.