Less than a week after drug lord Rafael Caro Quintero was released from prison because of procedural errors, the Mexican government is taking a second look.

Mexican Attorney General Jesus Murillo Karam said his office will review the decision of an appeals court to release the trafficker.

Caro Quintero had served 28 years when he was freed Friday because he was tried in the federal system, when his crimes should have been dealt with at the state level.

He was convicted of torturing and killing U.S. Drug Enforcement Administration agent Enrique "Kiki" Camarena in 1985, but the appeals court dismissed that conviction.

"I am studying the reasons of why he was freed," Murillo said. "The attorney general's office will use the resources available to it ... to avoid this type of impunity."

The attorney general spoke at a conference in Mexico City.

Afterward, he told journalists that there was no extradition request in place at the time that Caro Quintero was freed, and it is unclear whether any such request has been filed since last week, according to the state-run Notimex news agency.

Caro Quintero remained on the DEA's most-wanted list during his incarceration in Mexico.

Because the appeals court had vacated his conviction for Camarena's murder, any extradition request would have to be for other crimes, Murillo said, according to Notimex.

The ruling also dismissed accusations against Caro Quintero of the killings of two other Americans -- John Clay Walker of Minneapolis and Albert Radelat of Fort Worth. The family of one of the Americans killed says they were targeted in retaliation for DEA drug raids. A conviction for drug trafficking was upheld, but Caro Quintero had already completed the prison sentence for that crime, the ruling said.

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.

CNN's Rafael Romo contributed to this report.