Story highlights DEA: "Deeply troubled" by pending release, will work "vigorously" for U.S. prosecution

Rafael Caro Quintero is serving time for the kidnapping and murder of a U.S. agent

A court ruled that he was tried in the wrong judicial system in Mexico

As a result, his convictions are overturned; he is still wanted by the United States

Rafael Caro Quintero, wanted in the U.S. for the torture and killing of DEA agent Enrique Camarena, has been ordered released from a Mexican prison because of procedural errors in his case.

A federal court in the state of Jalisco overturned Caro Quintero's conviction for the kidnapping and killing the U.S. agent in 1985. The court ruled that the infamous drug lord was incorrectly tried in the federal judicial system, when he should have been tried at the state level.

The ruling also dismissed the cases of two other killings that he was accused of.

A conviction for drug trafficking was upheld, but he has already completed the prison sentence for that crime, the ruling said.

The U.S. Drug Enforcement Administration issued a statement Friday saying it was "deeply troubled" by the apparently impending release of Caro Quintero, who the DEA called the "mastermind and organizer" of its agent's death.

The agency said it will "vigorously continue ... efforts to ensure Caro-Quintero faces charges in the United States for the crimes he committed."

The killing of Camarena, nicknamed "Kiki," strained relations between the United States and Mexico. In the eyes of the U.S. justice system, Caro Quintero remains an international fugitive, and his release would sting U.S. authorities.

But Mexican judicial authorities said in a statement that Caro Quintero's release is ordered "as long as there is no other legal reason to impede it."

It was unclear if U.S. efforts to extradite Caro Quintero would be considered legal impediments to his release.

Caro Quintero, who was arrested when he was 33, has spent the last 28 years in prison.

He was indicted in the Central District of California in 1988 on racketeering charges, which were eventually augmented with charges of kidnapping and murder of a federal agent.

A second indictment in the same district charges Caro Quintero with conspiracy to import and distribute cocaine and marijuana.

He also was indicted in the District of Arizona on drug trafficking charges.