Since 2006, more than a dozen of Colombia's most notorious paramilitary leaders have been extradited to the United States to face drug trafficking charges in U.S. District Court in Washington.

The extraditions stunned Colombians, who had hoped that testimony from the men, given as part of a national amnesty program, would help expose the truth about two decades of vicious murders, assaults and kidnappings. In videotaped confessions in Colombia, one had taken responsibility for more than 450 slayings.

But outrage over the extraditions reached a boiling point earlier this year when U.S. District Judge Reggie B. Walton blocked public access to seven of the paramilitary leaders' cases, erasing virtually every trace of their existence.

There is no way to know if the men have negotiated lenient sentences - or if they are even still in custody. An eighth defendant, accused in Colombia of murdering a judge, was released on his own recognizance, records show, after his cousins in College Park vouched for him.

The Colombian cases are drawing new attention to the practice of sealing entire court files, triggering a broader controversy over judicial secrecy.

Though court policies discourage this degree of secrecy, a 2009 internal study showed that federal judges order it in thousands of cases a year, sometimes without justification.

Some judges not only block public access but also remove file numbers and all other signs of a case from the record. In the D.C. district, there is no uniform procedure for sealing, leaving individual judges to decide how much to disclose, Chief Judge Royce C. Lamberth said.

The cases against the Colombian paramilitaries show the stakes of a transparency debate that might otherwise seem academic.

"More than anger, I feel powerless," said Bela Henriquez, whose father, Julio, was kidnapped and killed on the orders of one defendant. "We don't know what they are negotiating, what conditions they are living under. What guarantee of justice do we have?"

The Supreme Court has ruled that public access to court cases is protected by the First Amendment because it is a crucial check on judicial power.

But some factors - national security material, an ongoing government investigation, vulnerable witnesses or victims - can justify secrecy.

The cases involving the Colombians were probably sealed to protect their safety, because they are cooperating with U.S. drug enforcement authorities, several former prosecutors said. "It's very possible," Lamberth said. U.S. prosecutors, defense attorneys and Walton declined to comment.