A Mexican drug kingpin convicted in the 1985 killing of a DEA agent was added Thursday to the FBI’s list of most-wanted fugitives — the 518th addition to the list.

Officials have said it’s the first time a suspect sought by the DEA was added to the FBI’s list. Rafael Caro-Quintero has controlled the Sinaloa Cartel along with Ismael “El Mayo” Zambada Garcia since the arrest of Joaquin “El Chapo” Guzman in 2016.

Caro-Quintero was released mistakenly from a Mexican prison in 2013 while serving a 40-year sentence for the kidnapping and murder of DEA Special Agent Enrique Camarena Salazar.

“We believe [the killer] is still in Mexico,” FBI Deputy Director David Bowdich said at a news conference.

Salazar was a Marine, fireman, police officer and deputy sheriff who was extremely close to unlocking a million‐dollar drug pipeline from Mexico to the U.S. in 1985 before he was abducted and killed in Mexico, according to the FBI.

Bowdich said the most-wanted list is “one of our most valuable tools,” and that 484 of the 518 fugitives who have been on the list have been captured.

“The U.S. Marshals remain steadfast in the pursuit of justice for our brother, DEA Special Agent Kiki Camarena,” U.S. Marshals Associate Director for Operations Derrick Driscoll said in a statement to the FBI. “We will continue to leverage all resources and work with our law enforcement partners here and in Mexico to develop the information that will lead to the capture of Rafael Caro-Quintero.”

“The DEA is grateful for all of the federal law enforcement agencies that have committed to pursuing Rafael Caro‐Quintero until the moment he is captured and returned to his rightful place in prison,” DEA Acting Administrator Robert W. Patterson said in a statement to the FBI.

Officials also increased the reward for Caro-Quintero’s capture to $20 million. James Walsh, a deputy assistant secretary for the State Department, said the amount was the highest offered by the Narcotics Reward Program, and the highest among the 33 active targets.

The feds also unsealed Thursday an additional indictment against Caro-Quintero, accusing him of trafficking in methamphetamine, heroin, cocaine and marijuana from 1980 until 2017.

The Associated Press contributed to this report.