Jaime J. Zapata, an American immigration agent killed in February.
As the United States has opened new law enforcement and intelligence outposts across Mexico
in recent years, Washington’s networks of informants have grown there
as well, current and former officials said. They have helped Mexican
authorities capture or kill about two dozen high-ranking and midlevel
drug traffickers, and sometimes have given American counternarcotics
agents access to the top leaders of the cartels they are trying to
dismantle. Typically, the officials said, Mexico is kept in the dark about the United States’ contacts with its most secret informants — including Mexican law enforcement officers, elected officials and cartel operatives — partly because of concerns about corruption among the Mexican police, and partly because of laws prohibiting American security forces from operating on Mexican soil.
“The Mexicans sort of roll their eyes and say we know it’s happening, even though it’s not supposed to be happening,” said Eric L. Olson, an expert on Mexican security matters at the Woodrow Wilson Center.
“That’s what makes this so hard,” he said. “The United States is using tools in a country where officials are still uncomfortable with those tools.”
In recent years, Mexican attitudes about American involvement in matters of national security have softened, as waves of drug-related violence have left about 40,000 people dead. And the United States, hoping to shore up Mexico’s stability and prevent its violence from spilling across the border, has expanded its role in ways unthinkable five years ago, including flying drones in Mexican skies.
The efforts have been credited with breaking up several of Mexico’s largest cartels into smaller — and presumably less dangerous — crime groups. But the violence continues, as does the northward flow of illegal drugs.
While using informants remains a largely clandestine affair, several recent cases have shed light on the kinds of investigations they have helped crack, including a plot this month in which the United States accused an Iranian-American car salesman of trying to hire killers from a Mexican drug cartel, known as Los Zetas, to assassinate the Saudi ambassador to Washington.
American officials said Drug Enforcement Administration informants with links to the cartels helped the authorities to track down several suspects linked to the February murder of a United States Immigration and Customs Enforcement agent, Jaime J. Zapata, who is alleged to have been shot to death by members of Los Zetas in central Mexico.
The D.E.A.’s dealings with informants and drug traffickers — sometimes, officials acknowledged, they are one and the same — are at the center of proceedings in a federal courthouse in Chicago, where one of the highest-ranking leaders of the Sinaloa cartel is scheduled to go on trial next year.
And last month, a federal judge in El Paso sentenced a midlevel leader of the Sinaloa cartel to life in prison after he was found guilty on drug and conspiracy charges. He was accused of working as a kind of double agent, providing the Immigration and Customs Enforcement agency with information about the movements of a rival cartel in order to divert attention from his own trafficking activities.
As important as informants have been, complicated ethical issues tend to arise when law enforcement officers make deals with criminals. Few informants, law enforcement officials say, decide to start providing information to the government out of altruism; typically, they are caught committing a crime and want to mitigate their legal troubles, or are essentially taking bribes to inform on their colleagues.
Morris Panner, a former assistant United States attorney who is a senior adviser at the Center for International Criminal Justice at Harvard Law School, said some of the recent cases involving informants highlight those issues and demonstrate that the threats posed by Mexican narcotics networks go far beyond the drug trade.
“Mexican organized crime groups have morphed from drug trafficking organizations into something new and far more dangerous,” Mr. Panner said. “The Zetas now are active in extortion, human trafficking, money laundering, and increasingly, anything a violent criminal organization can do to make money, whether in Mexico, Guatemala or, it appears, the U.S.”
