Indefinite detention without trial is illegal under international law, but that’s slim comfort for the 35 men being held at Guantánamo with no prospect of release or a day in court. (A further two dozen men remain in legal limbo, recommended for trial by a federal task force five years ago but not yet charged.) The 35 “forever” prisoners are men the U.S. deems too dangerous to release but is reluctant to try in court. Under international law of war, goes the official line in Washington, these detainees are not entitled to trials.

Asked why the 35 can’t be prosecuted, Pentagon spokesman Lt. Col. Myles Caggins told Al Jazeera, “the evidence [against them] may not be legally sufficient.” But their continued detention remains one of the key obstacles to President Barack Obama’s goal of closing the prison.

The identities of the indefinite detainees (48 men at the time) were released in the summer of 2013 after a Freedom of Information Act request. Two died by the time the list was made public, and since then, several have been released or moved to the cleared-for-release list by the Periodic Review Board (PRB), established by Obama with an executive order in 2011.

The PRB does “not address the legality of any individual’s detention,” according to an official statement but considers “the threat posed by each detainee under review.” The six-agency board consists of officials from the Joint Staff, the Office of the Director of National Intelligence and the Defense, Homeland Security, Justice and State departments. The panel began reviewing prisoners in November 2013. But it has done little to expedite closing the prison. By the end of 2014, fewer than a dozen men had been reviewed — of whom six were cleared for release.

As the American Civil Liberties Union noted, at the PRB’s current rate of processing, “it will take at least six years to complete the first review of eligible detainees.”

The ACLU believes that anyone not charged with a crime should be transferred from the prison. “If the PRBs continue to be a way for the Defense Department to clear detainees for transfer, then they must be expedited, which will require a commitment of greater resources, including for the legal representation of detainees,” Chris Anders, senior legislative counsel in the ACLU’s Washington legislative office, wrote via email.

Caggins said the PRB process would be accelerated in 2015, which “may result in a greater number of detainees being cleared.”

Fawzi al-Odah was one of the more fortunate “forever” prisoners, having been reviewed, cleared and then repatriated to Kuwait in 2014. He was never charged during his 13 years in captivity, nor was there any explanation of why the U.S. had considered him a threat and then suddenly reversed itself. The review board concluded that the continued detention of the last remaining Kuwaiti, Fayiz al-Kandari, was necessary. This despite the fact that both men’s stories — and publicly available Department of Defense files — are nearly identical.

Yemeni Abdel Malik Ahmed Abdel Wahah al-Rahabi also faced the PRB twice in 2014. The first time, the board mandated his continued detention, but later in the year, it decided “continued law of war detention of the detainee is no longer necessary” and cleared him for release.

“He lost, but we somehow convinced the board to reverse its decision,” said his lawyer David Remes. “You can say all you want that (the prisoner) is there on the basis of lies against him, that it’s mistaken identity,” Remes said, “but the fact remains that the U.S. is going to stick by its narrative about what happened in the past. And the only hope is persuading the PRB that its security concerns about the future are unwarranted.” The Catch-22, Remes added, is that his client had never done what he was accused of doing.

Most of the Defense Department files released by WikiLeaks accuse these “forever” prisoners of being members of — or affiliated with — Al-Qaeda or the Taliban, citing allegations made by prisoners held in Guantánamo. But it’s not hard to see from the publicly available evidence why the military has concluded that it would be difficult to obtain a conviction in many cases.

The accuracy of the government’s evidence against Saudi Mohammed al-Shimrani, 39, is questionable, despite the fact that the PRB decided on Oct. 3, 2014 to continue holding him. Most of the information in his Department of Defense report, released via WikiLeaks, came from Shimrani himself and from several other prisoners whose testimony has been deemed unreliable because of the circumstances under which it was extracted.

Additionally, the CIA held eight of the “forever” prisoners, including a few men considered high-value-detainees such as Mohammed Rahim al-Afghani from Afghanistan and Hassan Guleed from Somalia. The integrity of their cases is questionable.

Carlos Warner, a federal public defender, represents Afghani as well as two other prisoners that remain on the indefinite detention list — Yemeni Abdul Rahman Ahmed and Kenyan Abdul Malik. “Some men lose hope and some hang on to whatever shred of hope exists,” he said. “Some look forward to Periodic Review Board hearings, while some believe these hearings will also be a farce. Every legal proceeding involving Guantanamo has been historically farcical, so it is difficult to argue with those men who have no hope for the future.”

The end of the U.S. combat mission in Afghanistan also opens up legal possibilities. In the Guantánamo habeas corpus cases in federal court, the Department of Justice has cited the Authorization of Military Force — the legal basis for the U.S. war in Afghanistan — as reason to hold prisoners. “There is no requirement that the day the war ends you have to turn everybody loose, but you have to begin making arrangements … in that direction, “ said Morris Davis, a retired U.S. Air Force colonel and the former chief prosecutor for the military commissions at Guantánamo. “Under the literal reading of the law, you can’t keep people forever once the war officially comes to an end.”

There is the statistical likelihood that some of the men released from Guantánamo may commit crimes when released. Addressing those fear Morris said, “We are never going to reduce the risk to zero ... We release people from [U.S.] prison all the time, and our recidivism rate is much higher than the recidivism rate at Guantánamo,” which is some 6 percent, according to Cliff Sloan, a former State Department Guantánamo envoy. “But you don’t keep people in prison past the end of their sentence,” Morris added, “just because people think there is a good chance that they are going to do something bad.” But that’s not the fate of the Guantánamo “forevers” — because they have no sentences to complete.