One of the most notorious drug chiefs in Mexico’s history, Osiel Cardenas, was released from a US prison on Friday into the custody of immigration officials who may deport him.

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

It was not clear if Cardenas will be deported to Mexico, or remain on US soil.

An ICE spokesperson said its Enforcement and Removal Operations officers took custody of Cardenas at the prison in Terre Haute, Indiana, and “he remains in ICE custody pending a final disposition determination”.

Citing an anonymous US official, NBC reported that the Biden administration plans to hand over Cardenas to Mexico on Monday.

Cardenas has outstanding charges in Mexico and is being held in a migration detention center in the US, a Mexican government source said.

Leo Silva, a former US Drug Enforcement Administration 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.