GUANTÁNAMO BAY, Cuba — A Yemeni prisoner at Guantánamo Bay who was cleared for release nearly a year ago scolded an Army judge on Friday and refused to testify in the U.S.S. Cole bombing case, fearing he would place himself in jeopardy after 20 years of U.S. detention.

“I am not here for you to take what you want from me, then throw me in the trash,” Abdulsalam al-Hela, who is in his 50s, said in his first appearance at the war court. “I have been waiting 20 years for justice.”

Mr. Hela was called as a would-be witness, not a defendant. He told the judge, Col. Lanny J. Acosta Jr., that he was concerned that “there are some evil people here” who would use his testimony against him.

Defense lawyers for Abd al-Rahim al-Nashiri, a Saudi prisoner, sought Mr. Hela’s testimony to try to help exonerate their client. Mr. Nashiri is accused of orchestrating the Qaeda suicide bombing of the Cole off Yemen in October 2000, which killed 17 U.S. sailors.

Mr. Hela was captured in Cairo in September 2002 — in court he said he had been “kidnapped” — and was held by the C.I.A. in its secret overseas black site network for about two years. He was brought to Guantánamo in September 2004 but has never been charged with a crime.

He was called two days in a row to testify in a deposition that could someday be used at Mr. Nashiri’s death penalty trial.

On Thursday, Mr. Hela refused to leave his prison cell to come to the court compound at Guantánamo Bay, called Camp Justice. On Friday, he came to court but refused to swear that he would tell the truth.

“He is afraid his answers will be used against him,” said a military defense lawyer, Maj. Michael J. Lyness of the Army, who told the judge that the prisoner was in effect invoking a privilege to not testify for fear of self-incrimination.

The judge agreed with that interpretation of the prisoner’s lecture and defiance, and he released Mr. Hela from an obligation to testify.

Mr. Hela is also at the center of a federal appeals court case considering the due process rights of wartime prisoners at Guantánamo who are not charged with war crimes.

U.S. intelligence agencies in 2020 described him as a “prominent extremist facilitator” who had “unspecified ties to Osama bin Laden and may have played a role in the attack on the U.S.S. Cole.”

In June, however, the interagency Periodic Review Board noted that Mr. Hela “lacked a leadership role in extremist organizations” and approved his transfer to the custody of another country. He has had no immediate place to go because U.S. law prohibits repatriation of Guantánamo detainees to war-torn Yemen, and U.S. diplomats are still trying to find an ally willing to receive him and monitor his activities.

The board recommended that he be resettled in a country that would let his family join him. It also recommended that the receiving country give Mr. Hela “reintegration support” and provide the United States with security assurances, meaning he would probably be forbidden from traveling outside that country.

The episode this week pointed to the frailties of the military commissions system. Before Mr. Hela agreed to come to court, the Army judge and lawyers in the case debated the judge’s authority to enforce a subpoena on the detainee because, although he is in the custody of the U.S. military, he is being held on foreign soil.

One of Mr. Nashiri’s defense lawyers, Katie Carmon, who sought the subpoena, said the war court was in “occupied territory.”

The lead prosecutor, Mark A. Miller, a Justice Department lawyer assigned to the Cole case, said: “We are leery of the notion that a subpoena can be issued by any court, American court, to a foreign national who is in a foreign country in a court that’s sitting in a foreign land. So I think the subpoena actually, for our purposes and to get this done, is kind of a waste of time.”

The office of the overseer of military commissions, known as the convening authority, refused to grant Mr. Hela immunity from prosecution in exchange for his testimony.

Ms. Carmon said the inability to get testimony from the Yemeni prisoner “robs both the defense and the American people of a public determination of where responsibility for the bombing of the Cole truly lies.”

In court, Mr. Hela spoke bitterly about his 20 years in U.S. custody, saying it was “like a life sentence.”

His lawyer, Beth D. Jacob, has said that he wants to be reunited with his wife and to be able to see his sole surviving child, a daughter he last saw when she was a toddler. His two sons were killed in an accident while he was held at Guantánamo, and the daughter, who is now married and expecting his first grandchild, is in Yemen studying to be a lawyer with a specialty in human rights.

The testimony capped two weeks of pretrial hearings that focused on the torture of Mr. Nashiri during his time in C.I.A. custody after his capture in Dubai in 2002 and of another Saudi prisoner who has admitted to being part of a Qaeda cadre that plotted attacks on seaborne vessels.