A criminal court in the western state of Jalisco approved Rafael Caro Quintero's release on August 7, a court official who asked not to be identified told AFP.

Caro Quintero has served 28 years in prison for the 1985 murder of US Drug Enforcement Administration special agent Enrique Camarena, who was kidnapped in Guadalajara and tortured and murdered.

The 60-year-old drug lord was informed of the court order early Friday but was awaiting a report from the Mexican federal attorney general on whether any other charges or extradition requests were pending against him, the court official said.

Mexico's federal prosecutors' office had no immediate comment.

At least as of June, Caro Quintero was still wanted in California on charges related to the Camarena murder and to drug trafficking.

The court official said one reason the judge ordered his release was because he had been tried in a federal court when his case should have been handled by a common criminal court.

"Camarena was not accredited as either a diplomatic nor a consular agent," the official said.

Camarena's killing produced sharp tensions between the United States and Mexico, which experts say wound up leading to closer cooperation between the two countries on drug trafficking cases.

Born in 1952 in the northwestern state of Sinaloa, Caro Quintero came from a town that has produced many of Mexico's notorious drug lords, including Joaquin "El Chapo" Guzman, head of the Sinaloa cartel and currently the most wanted man in Mexico.

Known as a "narco's narco," he went on to found the Guadalajara cartel with two other partners.

They were the first to turn run-of-the-mill Mexican drug trafficking into a multinational business.

His fall began in November 1984 when Mexican authorities raided a ranch he owned with his partners in the northern state of Chihuahua and seized nearly 8,000 tons of marijuana.

In retaliation, Caro Quintero ordered Camarena's kidnapping and killing the following February.

Furious over his killing, the US government launched a covert operation inside Mexico, capturing a doctor who took part in Camarena's torture and spiriting him out of the country.

Less than a month after Camarena's murder, Caro Quintero was apprehended in bed with a girlfriend at a property in Costa Rica, and extradited to Mexico City.

He was imprisoned in the Puente Grande maximum security prison in Jalisco, where a former cellmate said he attended Sunday mass, read avidly about Mexican history, and jogged and played volleyball for exercise.

The Guadalajara cartel broke up after his arrest, but other major trafficking organizations rose up to replace it, unleashing a bloody struggle for control of smuggling routes into the United States.