MEXICO CITY (AP) — U.S. law enforcement officials are expressing outrage over the release of Mexican drug lord Rafael Caro Quintero from a prison in Mexico.

Caro Quintero was sentenced to 40 years in prison for the 1985 kidnapping and killing of DEA agent Enrique Camarena. But a Mexican federal court ordered his release this week saying he had been improperly tried in a federal court for state crimes.

The 60-year-old walked out of a prison in the western state of Jalisco early Friday after serving 28 years of his sentence.

The U.S. Department of Justice calls the decision "deeply troubling," while the DEA says it "will vigorously continue its efforts to ensure Caro-Quintero faces charges in the United States."

The Association of Former Federal Narcotics Agents in the United States blamed corruption within Mexico's justice system for Caro Quintero's early release.