MEDELLIN, Colombia: One of Colombia's most feared paramilitary warlords testified before a special tribunal Tuesday, a confession meant to sharply reduce any prison term for his role in the murders of hundreds of civilians during a decade-long reign of terror.

Salvatore Mancuso's confession was the first by a top militia commander as part of a 2003 peace deal with the government that led to the demobilization of 31,000 right-wing fighters.

Under the law that codified the peace pact, Mancuso and more than 2,000 strongmen from the United Self-Defense Forces of Colombia, or AUC, must offer detailed confessions of their involvement in massacres, torture and other crimes. Otherwise, they are not eligible for reduced jail terms — no more than eight years — and could be extradited to the United States on drug-trafficking charges.

Mancuso arrived at court under heavy police guard. About 30 relatives of victims were initially barred from the courthouse but were later allowed to watch Mancuso testify via closed-circuit television along with people who had filed formal complaints against the warlord. Representatives of human rights groups and the news media were not permitted entry.

"This is a farce," said Maria Victoria Fallon, a lawyer who has brought a case against Mancuso before the International Court of Justice for a 1997 massacre in which men under his command slaughtered 15 farmers in the northwestern hamlet of El Aro. A Colombian court in 2003 convicted Mancuso in absentia in the El Aro massacre, sentencing him to 40 years in prison.

Under the peace pact, Mancuso and other paramilitary warlords face a maximum of 5 to 8 years in prison for all their crimes.

Human rights groups say the government is being too lenient. Mancuso, whose violence-scarred fiefdoms encompassed much of northern Colombia, and other warlords blamed for some of the worst atrocities in Colombia's half century of civil conflict.

The rights groups also demand reparations, and placards hung outside the courthouse reflected those desires.

The peace process is a major test for President Alvaro Uribe, who has been dogged by a growing scandal linking several close political allies to the drug-funded AUC, which the United States lists as a "foreign terrorist organization."

Already, three pro-government federal lawmakers have been arrested for arming and financing the illegal militias, and at least a half dozen more, including the brother of Uribe's foreign minister, are under investigation.

That number could increase after Mancuso's testimony, which was expected to last several days, if he reveals the identities of the AUC's main political backers and beneficiaries.

"We have an opportunity to turn over a new leaf," Vice President Francisco Santos told The Associated Press in an interview last week. "It's going to be traumatic, but the whole truth must come out. We've got nothing to hide."

According to his Web site, Mancuso, 42, was a national motocross champion and studied English at the University of Pittsburgh before taking up arms in 1995 against leftist rebels who were extorting his fellow cattle ranchers in the state of Cordoba.

Like much of the AUC leadership, Mancuso soon strayed from the group's original aim, getting deep into Colombia's lucrative cocaine trade — for which he is wanted for extradition to the United States — and slaughtering enemies real or imagined while forcibly displacing tens of thousands from their lands.

With the future of the peace process now uncertain, the nation is waiting to see what paramilitary bosses like Mancuso say in court.

Many Colombians believe the warlords plan to divulge only what prosecutors already know about their crimes while secretly shuttling huge fortunes overseas and maintaining lucrative cocaine-smuggling operations.

Critics also say the government, whose soldiers and police colluded with the paramilitaries in their zones of influence, has not provided enough guarantees so victims feel safe enough to come forward with their testimony.

"There's a lot of fear among victims," said human rights activist Ivan Cepeda, whose father, a former leftist senator, was slain by paramilitary gunmen in 1994. "Especially in remote areas, people can see with their own eyes that the paramilitary apparatus continues operating."

For their part, Mancuso and 58 other jailed warlords have accused the government of double-crossing them by transferring them from a resort-turned-prison to the maximum-security Itagui facility near this western city on Dec. 1.

The paramilitaries also have complained of death threats against them and family members by people they claim want to silence the truth-telling even before it begins.

Even from a cinderblock cell, Mancuso remains a powerful figure — and a hero to many.