Osiel Cárdenas Guillén, a former drug cartel leader described as having “generated a new era of organized crime” in Mexico, has now been released from U.S. prison and may be heading back over the border, reports say. 

Cárdenas Guillén, the past leader of the Gulf cartel who created the Zetas — a gang of former Mexican special forces soldiers who became his private army and hit squad — was transferred into the custody of U.S. Immigration and Customs Enforcement on Friday at a federal prison in Terre Haute, Indiana, officials told Reuters. 

In 2010, Cárdenas Guillén was sentenced to 25 years in prison on charges including threatening to assault and murder federal agents and was ordered to forfeit $50 million from his criminal enterprise. It’s unclear why he did not serve his full sentence. However, the move into ICE custody suggests he will be deported to Mexico, where an official says he faces two arrest warrants, according to The Associated Press. 

Leo Silva, a former U.S. Drug Enforcement Administration agent who previously worked in Mexico to combat the Zetas, told Reuters that the Cárdenas Guillén “generated a new era of organized crime” and “unleashed this mentality of creating fear in the country.” 

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The news agency cites Silva as directly blaming Cárdenas Guillén for the rise in grisly cartel-related violence in Mexico over the last 20 years. 

The Zetas that he created committed acts of terror that regularly involved slaughtering dozens of people, decapitating them or dumping heaps of hacked-up bodies on roadways, The Associated Press reports. 

Cárdenas Guillén’s own nickname was “El Mata Amigos,” or “The one who kills his friends,” and the 57-year-old once moved tons of cocaine and made millions of dollars through the Gulf cartel, based in the border cities of Reynosa and Matamoros. 

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He was eventually captured in 2003 and extradited to the U.S. four years later. By 2010, the Zetas had formed their own cartel, spreading terror-style attacks across Mexico as far south as Tabasco until their top leaders were killed or arrested in 2012-2013. 

The AP reports that one of Cárdenas Guillén’s most brazen acts was when he surrounded and stopped a vehicle carrying two U.S. DEA agents and one of their informants in 1999 in the border city of Matamoros, across from Brownsville, Texas. 

His gunmen pointed their weapons at the agents and demanded they hand over the informant, who would almost certainly be tortured and killed. The agents toughed it out and refused, reminding him it would be a bad decision to kill employees of the DEA. Cárdenas Guillén eventually called off his gunmen, but not before reportedly saying “You gringos, this is my territory.” 

The Associated Press contributed to this report.