Mexico’s Curbs on U.S. Role in Drug Fight Spark Friction

MEXICO CITY — In their joint fight against drug traffickers, the United States and Mexico have forged an unusually close relationship in recent years, with the Americans regularly conducting polygraph tests on elite Mexican security officials to root out anyone who had been corrupted. 

But shortly after Mexico’s new president, Enrique Peña Nieto, took office in December, American agents got a clear message that the dynamics, with Washington holding the clear upper hand, were about to change  “So do we get to polygraph you?” one incoming Mexican official asked his American counterparts

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A Drug War Informer in No Man’s Land

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.

Monica Almeida/The New York Times

From Informant to Fugitive Mr. López was once a powerful police chief in Mexico and a valued D.E.A. informant. Today he is a fugitive, sought by the Mexican government after the arrest of his boss, Mexico’s former drug czar.

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 http://www.nytimes.com/2013/04/29/us/us-mexico-dea-informant.htmlthe case; the D.E.A. saw him as a potential gold mine of information.

The United States found him first.....