[Source: Reuters]

One of the most notorious drug chiefs in Mexico’s history, Osiel Cardenas, was released from a U.S. prison into the custody of immigration officials, the U.S. Federal Bureau of Prisons said.

Former leader of the Gulf Cartel, Cardenas presided over some of the bloodiest gang violence in Mexico’s turbulent past and has been blamed for transforming drug trafficking by embracing hyper-violent tactics such as decapitations.

Cardenas founded the Zetas, an armed wing of the Gulf Cartel made up of former army special forces.

He was captured after a gun battle in 2003 and extradited to the United States in 2007. He was sentenced to 25 years in prison in 2010.

The Zetas later branched off on their own and became, for a while, the most deadly crime group in Mexico before largely fizzling out.

A spokesperson for the U.S. prison service told Reuters Cardenas was released “into the custody of U.S. Immigration and Customs Enforcement (ICE)” earlier on Friday.

It is not clear if Cardenas will be deported to Mexico, or remain on U.S. soil.

Cardenas has outstanding charges in Mexico and is currently in a migration detention center in the U.S., a Mexican government source said.

Leo Silva, a former U.S. Drug Enforcement Administration (DEA) agent who worked in Mexico countering the Zetas, said Cardenas was directly to blame for the upturn in grisly violence in Mexico over the past two decades.

The Zetas pioneered efforts by organized crime groups to branch out from simply trafficking drugs to also extorting residents and businesses in areas they controlled.

The Zetas also sowed terror by widely kidnapping for ransom.

“This was something that Osiel created that generated a new era of organized crime,” said Silva, who worked for the DEA in Mexico from 2008-2015.

“He unleashed this mentality of creating fear in the country.”