Infamous drug lord Rafael Caro Quintero walked free Friday after 28 years in prison when a court overturned his 40-year sentence for the 1985 kidnap and killing of a U.S. Drug Enforcement Administration agent, a brutal murder that marked a low point in U.S.-Mexico relations.

The court ruled that Caro Quintero was improperly tried in a federal court for the crime that should have been treated as a state offense. Prison officials were notified of the ruling on Thursday, and an official at the Jalisco state prosecutors’ office said the 61-year-old drug lord left prison before dawn on Friday. The official was not authorized to speak on the record.

News media were not alerted until hours after the release, and it was unclear whether U.S. authorities had received prior notification.

Caro Quintero still faces active charges in the United States and Mexico’s Attorney General’s Office said it did not know if there was a current extradition request.

The U.S. Embassy in Mexico did not immediately comment on the release or court ruling, which came on Wednesday.

Caro Quintero is considered the grandfather of Mexican drug trafficking. He established a powerful cartel based in the northwestern Mexican state of Sinaloa that later split into some of Mexico’s largest cartels, including the Sinaloa and Juarez cartels.

Caro Quintero is still listed as one of the DEA’s five top international fugitives, and U.S. authorities believe he continued to control the laundering of drug money from behind bars.

“Caro Quintero continues to launder the proceeds from narcotics trafficking and he maintains an alliance with drug trafficking organizations such as the Sinaloa Cartel, most notably with Esparragoza Moreno’s network,” said Treasury Department spokesman John Sullivan, referring to Juan Jose Esparragoza Moreno — also known as “El Azul,” or “Blue” because of the dark color of his skin — who is allegedly a top leader of the Sinaloa cartel.

In June, the Treasury Department imposed sanctions against 18 people and 15 companies that allegedly moved money for Caro Quintero.

Mexico’s relations with Washington were badly damaged when Caro Quintero ordered undercover agent Enrique Camarena kidnapped, tortured and killed, purportedly because he was angry about a raid on a 220-acre marijuana plantation in central Mexico named “Rancho Bufalo” that was seized by Mexican authorities at Camarena’s insistence.

Camarena was kidnapped on Feb. 7, 1985, in Guadalajara, a major drug trafficking center. His body and that of his Mexican pilot, both showing signs of torture, were found a month later, buried in shallow graves.

American officials accused their Mexican counterparts of letting Camarena’s killers get away. Caro Quintero was eventually hunted down in Costa Rica.

At one point, U.S. Customs agents almost blocked the U.S. border with Mexico, slowing incoming traffic to a standstill while conducting searches of all Mexicans trying to enter the United States.

Camarena’s fellow DEA agents consider him a hero in the war against drug trafficking and the El Paso Intelligence Center, where U.S. federal agencies collect information about Mexican drug barons, is dedicated to him.

Caro Quintero is said to have pioneered links between Colombian cocaine cartels and the Mexican smugglers who transport their drugs into the United States.

The ruling left many wondering why it took 24 years for judges to determine Caro Quintero was tried in the wrong court.

“What appears to be coming is an avalanche of judicial appeals, with the drug traffickers hiring very good, very expensive lawyers, arguing there were violations of due process,” said Raul Benitez, a security expert at Mexico’s National Autonomous University. “The government is going to have problems.”