A former leader of a Mexican drug cartel who ushered in a new era of organized crime has been released from a US prison.

Reports indicate that Osiel Cárdenas Guillén, a former drug cartel leader who is said to have ushered in a new era of organized crime in Mexico, has been released from a U.S. prison and may be returning to Mexico.

On Friday, Cárdenas Guillén, the former leader of the Gulf cartel who formed the Zetas, a group of ex-Mexican special forces soldiers who served as his private army and hit squad, was handed over to U.S. Immigration and Customs Enforcement at a federal prison in Terre Haute, Indiana, according to officials.

In 2010, Cárdenas Guillén was convicted of threatening to assault and murder federal agents and was sentenced to 25 years in prison. He was also ordered to forfeit $50 million from his criminal enterprise. Despite this, it is unclear why he did not serve his full sentence. However, his recent move into ICE custody indicates that he will be deported to Mexico, where an official states that he faces two arrest warrants, according to The Associated Press.

A former U.S. Drug Enforcement Administration agent who previously worked in Mexico to combat the Zetas, Leo Silva, stated that the Cárdenas Guillén "created a new era of organized crime" and "instilled a fear-mongering mentality in the country."

Cárdenas Guillén is directly blamed by Silva for the increase in cartel-related violence in Mexico over the past 20 years, according to the news agency.

According to the Associated Press, the Zetas, a group created by the individual, were responsible for acts of terror that frequently resulted in the slaughter of dozens of people, their decapitation, or the dumping of heaps of mutilated bodies on roadways.

Reynosa and Matamoros-based Gulf cartel member Cárdenas Guillén, known as "El Mata Amigos," or "The one who kills his friends," moved tons of cocaine and made millions of dollars.

In 2003, he was captured and extradited to the U.S. By 2010, the Zetas formed their own cartel, carrying out terror-style attacks in Mexico until their leaders were killed or arrested in 2012-2013.

In 1999, in the border city of Matamoros, across from Brownsville, Texas, one of Cárdenas Guillén's most daring actions was stopping a vehicle carrying two U.S. DEA agents and one of their informants.

Cárdenas Guillén's gunmen aimed their weapons at the DEA agents and demanded they surrender the informant, who was likely to be tortured and murdered. Despite the threat, the agents remained resolute and refused, reminding Cárdenas Guillén that killing DEA employees would be a poor decision. Eventually, Cárdenas Guillén withdrew his gunmen, but not before reportedly saying, "This is my territory, gringos."

The Associated Press contributed to this report.