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A Colombian warlord who has cooperated closely with prosecutors was extradited to the United States on Thursday despite human rights groups' objections that sending him away could leave hundreds of murders unsolved.

Heberth Veloza, alias "HH," has admitted to personally killing more than 100 people and has acknowledged that fighters under his command killed hundreds more. He is the 17th Colombian paramilitary boss to be extradited to the United States in less than a year to face drug-trafficking charges.

Handcuffed and wearing a bulletproof vest under a dark jacket, Veloza departed for New York on a DEA Super King turboprop plane accompanied by four U.S. agents. He switched planes at Guantanamo Bay, Cuba, U.S. and Colombian officials said.

Veloza, 41, was a top lieutenant of the Castano brothers, co-founders of Colombia's far-right militias in the 1980s. Initially backed by drug traffickers and ranchers to counter kidnapping and extortion by leftist rebels, the private armies evolved into regional mafias.

Prosecutors say they committed well over 10,000 murders and stole millions of acres of land, often in collusion with local political, business and military leaders.

Captured in April 2007, Veloza is among jailed warlords who have cooperated most with prosecutors under a law that offers reduced sentences as part of a demobilization pact.

U.S. officials have vowed to give Colombian prosecutors ample access to imprisoned warlords, but human rights groups complain that Veloza's extradition — though it was delayed by six months at their request — will allow many crimes committed under his command to go unpunished. They say it also could prevent the recovery of hundreds of corpses still buried in unmarked graves.

"There was no reason for an extradition with such urgency," said Ivan Cepeda, spokesman for the National Movement of Victims of Crimes of the State. "We didn't ask that he not be extradited, just that it be delayed until he could confess to everything."

Prosecutor Nubia Chavez said Veloza has acknowledged 480 murders by fighters under his command, including the 2004 killing of the Castano brother Carlos, who was chief of the umbrella United Self-Defense forces of Colombia, or AUC.

"I think he was able to confess to about 50 percent of his crimes," Chavez told The Associated Press.

The chief prosecutor in charge of Justice and Peace cases, Luis Gonzalez, says some 4,000 unmarked graves remain to be located and unearthed in Colombia.

Veloza personally led investigators to 32 unmarked graves that yielded 54 corpses, said Chavez.

His testimony has backed claims by human rights groups that Colombia's armed forces long cooperated with the illegal militias.

Among the military officers Veloza said helped right-wing death squads is retired army Gen. Rito Alejo del Rio, who was jailed in September on murder charges. Del Rio was a brigade commander in the banana-growing region of Uraba in the mid-1990s when Veloza was the chief warlord there.

Veloza also was among warlords who have testified that Chiquita Brands International made regular payments to the paramilitaries in Uraba.

Chiquita has acknowledged paying the AUC a total of $1.7 million from 1997-2004. It paid a $25 million fine in the United States and is fighting lawsuits in the United States that seek to hold it responsible for hundreds of deaths.

On Wednesday, Colombia extradited Miguel Angel Mejia, another warlord indicted in the United States on drug trafficking charges.

Both men initially surrendered under the peace pact, only to return to fugitive life.

In all, nearly 900 criminal suspects have been extradited to the United States under Uribe, the vast majority on drug trafficking charges.