....Mr. López played a leading role in what is widely considered the biggest drug-trafficking case in Mexican history. The episode — which inspired the 2000 movie “Traffic” — pitted the Mexican military against the United States Drug Enforcement Administration. Throughout the 1990s, Mr. López worked closely with them both. He served as a senior adviser to the powerful general who was appointed Mexico’s drug czar. And he was an informant for the D.E.A.
His two worlds collided spectacularly in 1997, when Mexico arrested the general, Jesús Gutiérrez Rebollo, on charges of collaborating with drug traffickers. As Washington tried to make sense of the charges, both governments went looking for Mr. López. Mexico considered him a suspect in the case; the D.E.A. saw him as a potential gold mine of information.
The United States found him first. The D.E.A. secretly helped Mr. López and his family escape across the border in exchange for his cooperation with its investigation.
Dozens of hours of testimony from Mr. López about links between the military and drug cartels proved to be explosive, setting off a dizzying chain reaction in which Mexico asked the United States for help capturing Mr. López, Washington denied any knowledge of his whereabouts and the D.E.A. abruptly severed its ties with him.
The reserved, unpretentious husband and father of three has been a fugitive ever since, on the run from his native country and abandoned by his adopted home. For more than a decade, he has carried information about the inner workings of the drug war that both governments carefully kept secret.
The United States continues to feign ignorance about his whereabouts when pressed by Mexican officials, who still ask for assistance to find him, a federal law enforcement official said.
The cover-up was initially led by the D.E.A., whose agents did not believe the Mexican authorities had a legitimate case against their informant. Other law enforcement agencies later went along, out of fear that the D.E.A.’s relationship with Mr. López might disrupt cooperation between the two countries on more pressing matters.
“We couldn’t tell Mexico that we were protecting the guy, because that would have affected their cooperation with us on all kinds of other programs,” said a former senior D.E.A. official who was involved in the case but was not authorized to speak publicly about a confidential informant. “So we cut him loose, and hoped he’d find a way to make it on his own.”
These are the opaque dynamics that undermine the alliance between the United States and Mexico in the war on drugs, a fight that often feels more like shadow boxing. Though the governments are bound together by geography, neither believes the other can be fully trusted. Mr. López’s ordeal — pieced together from classified D.E.A. intelligence reports and interviews with him, his family, friends, and more than a dozen current and former federal law enforcement officials — demonstrates why the mutual distrust is justified....
....In January, the Mexican government once again raised Mr. López’s case with the American authorities, according to a Mexican official. The Justice Department asked for confirmation that the charges against Mr. López were still valid, and the Mexican government is expected to report back within the coming weeks, the Mexican official said.
“Until then,” he said, “the case is not closed, as far as we are concerned.”
The Justice Department and the D.E.A. said they could not comment on a case that involved a confidential informant. But an American law enforcement official who has fielded some of Mexico’s requests said Washington was stalling for time, hoping the charges would be dropped. The United States is no closer to understanding whether Mr. López is guilty or the target of Mexican officials who wanted to silence him, the American official said.
“If it was up to us, we’d make this case go away,” the official said. “But if Mexico decides it still wants him, I’m not sure how the United States is going to say no.”
Security cooperation between the United States and Mexico has been strained since December, when Enrique Peña Nieto began his term as president of Mexico. His administration believes that his predecessor, Felipe Calderón, allowed the United States to play too big a role in setting Mexico’s security agenda and in staging law enforcement operations, officials in both countries said.
The Obama administration has struggled to negotiate new terms of cooperation, the officials said, and President Obama is scheduled to travel to Mexico this week.
Meanwhile, the violence that has left about 60,000 people dead over the past five years rages on. And the military has been so demoralized by accusations of corruption and human rights abuses that some of its leaders openly wonder whether to pull out of the fight against drug traffickers.
Mr. López religiously tracks these developments during his morning coffee breaks at McDonald’s, looking for clues that might help him make sense of his own situation. Mr. Villarruel, now retired from the D.E.A., is one of his few contacts from his former life. Mr. López said he sees public attention as his only hope for a return to something resembling a normal existence. “For better or worse, it’s time that I defend myself,” Mr. López said.
When asked what he would do if he ran out of money, Mr. López shrugged and said he would figure something out. He compares himself to Prometheus, the Greek mythological figure whose punishment for stealing fire and giving it to humans was to be tortured, surviving only to face the same torment the next day.
“Every day is like the first day for me,” he said. “From the moment I wake up until the moment I lay down, I am thinking, thinking, thinking about what happened to me. I try to make sense of things that don’t make sense. And it eats away at me. And it eats away at my family. Then the next day, I wake up and start all over again.”
