WASHINGTON — The United States may not be allowed to keep a man imprisoned in Guantánamo Bay after he is no longer deemed a threat, the U.S. Court of Appeals for the D.C. Circuit ruled in an opinion released Wednesday. But the court disappointed advocates for prisoners by leaving unresolved the question of what constitutional protections he and other prisoners at the military facility have.

Instead, a divided court found that neither the two decades Abdulsalam Ali Abdulrahman Al-Hela has spent in detention nor the classified intelligence used to justify his detention violated due process as guaranteed by the Fifth Amendment, so it was unnecessary to say definitively whether he has that right.

"We assume without deciding that the Due Process Clause applies," Robert L. Wilkins, an Obama appointee, wrote for the court. Quoting the chief justice of the U.S. Supreme Court, he said, "This is the correct and most prudent course of action."

While the decision was made on April 4, the reasoning behind it was kept sealed until Wednesday.

Al-Hela, a businessman and tribal sheik from Yemen, was first captured in Egypt in 2002 and held overseas before being brought to Guantánamo two years later. He has been contesting his detention in court since 2005.

Without a ruling ordering his release, "Abdulsalam will continue to serve what amounts to a life sentence, as cruel in its own way as the horrific physical torture that he endured in the CIA' s 'dark prisons,'" his lawyers wrote in a court filing.

They said in a statement Wednesday that they "are disappointed that the Court did not order our client's release after the Government has held him for over 20 years without charge or trial."

A lower court judge, relying in part on classified intelligence information that was not shared with Al-Hela's attorneys, designated him as an enemy combatant based on evidence that he "facilitated the travel of Islamic extremists," including al-Qaeda members, and "provided logistical support . . . for several bombing attacks." Al-Hela argued that if he helped terrorists travel it was part of a government effort to get them out of Yemen, and that only "vague allegations" tie him to any bomb plot.

That hearing and decision "was thorough and carefully calibrated to minimize the risk of error without unduly burdening the Executive," the circuit ruled, noting that Al-Hela himself testified and U.S. District Court Judge Royce C. Lamberth scrutinized and sometimes rejected government requests for secrecy.

Jonathan Hafetz, a Seton Hall law professor and former national security attorney with the ACLU, called the decision disappointing and "unfortunate in many respects," because "the court once again ducked the major issue."

"It's a missed opportunity to declare that basic rights to due process applies to people the U.S. government has locked up for two decades in a U.S. offshore prison," he said.

Hafetz and other attorneys said there are also important issues not raised in Al-Hela's case - particularly after U.S. troop withdrawals from Iraq and Afghanistan. President Biden has also said he intends to close the offshore prison during his tenure; 31 detainees remain there as of March. (At its peak in 2003, Guantánamo held 684 detainees). Only two have been convicted of a crime.

"Even if Guantánamo detainees don't have due process rights, which hasn't been decided, they cannot be held as wartime detainees for a war that no longer exists as a legal and practical matter," Hafetz said.

Lawmakers are moving forward with President Biden's support to end authorization for the war in Iraq, but not the 2001 "war on terror" legislation used to justify detentions at Guantánamo.

The circuit returned Al-Hela's case to a lower court to decide whether he should be released because the United States no longer considers him a security threat. In 2021, the Periodic Review Board - a body composed of representatives from the CIA, the Defense Intelligence Agency, the Department of Homeland Security and the Justice Department - cleared Al-Hela for release as long as he is sent to a country that can employ "appropriate security measures." But his home country of Yemen is not considered safe.

At oral argument in 2021, the government asked the court for this narrow ruling and described the determination that Al-Hela can be released as irrelevant.

"The Biden administration continues to fight in court to detain an individual, who the government says it doesn't want to detain, in a prison the president says should be closed," said J. Wells Dixon, a senior staff attorney at the Center for Constitutional Rights.

He said the ruling raised "a significant legal question . . . does the Constitution allow the government to continue to hold someone without foreseeable end simply because it hasn't made sufficient efforts to transfer them?"

Any future appeals court ruling on that issue could impact 16 other detainees who are being held at Guantánamo despite being approved for transfer. Some have been in that limbo for over a decade.

When this case first came before the appellate court in 2020, Judge Neomi Rao wrote for the majority of a three-judge panel that as a "nonresident alien detained outside of U.S. sovereign territory" Al-Hela had no due process rights. Rao, a Trump appointee, wrote in dissent Wednesday that the court was "applying a watered-down version" of the Constitution "to accommodate the procedures applied at Guantanamo," which "threatens to undermine procedural protections in the very contexts where they actually apply."

She and the three other Republican appointees on the panel said they would uphold her ruling barring any due process claims for Guantánamo detainees.

"When an important and recurring but unresolved question is confronting our court, that is a reason for deciding the question en banc, not for evading it and perpetuating uncertainty," Judge A. Raymond Randolph, a George H.W. Bush appointee, wrote in his own dissent. "Alien enemies detained overseas are not 'persons' within the meaning of the Fifth Amendment's Due Process Clause."

He noted that the Supreme Court has recently indicated a willingness to reverse itself and close off federal courts to Guantánamo prisoners altogether, ruling in a 2020 immigration case that it is not clear whether noncitizens have the right to contest detention in federal court.

In 2008 the U.S. Supreme Court, overturning another decision written by Randolph, ruled 5 to 4 that Guantánamo detainees have the right to challenge their detention in federal court. But the details of the process were left to the D.C. Circuit court, which repeatedly interpreted the decision in ways that favored the government and denied detainees relief. When Asadullah Haroon Gul was ordered released by Judge Amit P. Mehta in 2021, it was the first successful habeas petition from Guantánamo in over a decade.

Many of those decisions came when the D.C. Circuit was dominated by conservatives; that is no longer the case. Three judges on the court - one appointed by Trump, two by Biden - did not participate in Al-Hela's appeal, and one Biden appointee heard argument on the case but has since been elevated to the U.S. Supreme Court, leaving a panel with a 6 to 4 majority of Democratic appointees.