This piece originally appeared in Foreign Policy on December 10, 2014.

On his first full day in office as president, Barack Obama signed an executive order to close the prison at Guantanamo Bay, Cuba. Nearly six years later, his administration has finally begun delivering on its promise. Sunday's transfer of six detainees to Uruguay brings the total number of detainees transferred since the beginning of November to 13 — more than the total number of transfers than took place in all of 2013 . That's a big deal. But let's not get ahead of ourselves.

While the administration has transferred detainees cleared for release in occasional bursts, it has failed to meaningfully address the plight of the more than 60 men held in indefinite detention without charge or trial. One cause of the failure is simple: in 2011 , the Obama administration designed an administrative hearing mechanism called the Periodic Review Board (PRB) to review the cases of indefinitely held detainees. But since then it has made only inconsistent, half-hearted use of this tool. And now time is running out.

Under the PRB's original mandate, representatives from six defense and intelligence agencies, including the Department of Justice and the Office of the Chairman of the Joint Chiefs, sit on the boards and review the cases of all detainees designated for continued detention who face neither charge nor conviction. The PRB would then make a transfer recommendation to the secretary of defense for detainees it determined no longer represented a threat to the United States.

Granted, the PRBs only hold administrative hearings and cannot correct the injustice of detention without charge or trial. But they are a key pathway to freedom for those detained indefinitely at Guantanamo.

Yet the board did not convene for the first time until Nov. 2013 — over a year and a half behind schedule . The PRBs also have a large task in front of them, as over 40 percent of the prison's 136 detainees are eligible for a review . And since the PRBs began, they have done little to advance efforts to close the prison. In many cases, detainees and their representatives are only allowed to see summaries of the government's evidence against them. Even worse, detainees without private lawyers must rely on representatives provided by the government who may not even have a legal background . Attorneys or not, these representatives are not allowed to make use of any evidence except for the material provided to them by board administrators.

Despite this bias at the core of the process, the review board has cleared five of the detainees who have appeared before it (the six released on Sunday were cleared for release in 2010, before the board). But that is out of only nine men who have been lucky enough to appear before the board, a telling reminder of how excruciatingly slow the PRB process has been.

When the PRBs first began in November of last year, 71 detainees were eligible for review; today, 57 are eligible for their first review, but have not yet received it (this accounts for five prisoners exchanged last summer whose cases weren't reviewed). At this rate, it will take at least six years to complete the first review of eligible detainees. Even then, a favorable decision would not guarantee a detainee's release. Sixty-eight detainees currently held at the prison are cleared for release, the vast majority of them since 2010 . Yet they remain behind bars.

Why the glacial pace? One rationale that NGOs monitoring the boards often hear from government representatives is that there's a lack of human resources. For each case the PRB hears, a special interagency body — the " Analytic Task Force " (ATF) — must compile all information relevant to the detainee's case and develop a summary of it. But according to government sources, there is no easy way to translate additional dollars for PRB operations into a faster pace for hearings given the unique mix of skillset, experience, and security clearance ATF staff need. Their hands are tied.

The excuse is as implausible as it is disappointing. In fact, four years ago, the Guantanamo Review Task Force — a separate interagency body created just days after the Obama administration took office to determine which detainees should be released, tried, or detained indefinitely — reviewed all 240 Guantanamo detainee cases. That process took just one year to complete. But while the task force designated 126 detainees as cleared for transfer, the majority of them remain at Guantanamo to this day. Then in 2013, the president appointed two envoys to oversee the prison's closure. Finally, the PRB process began later that year to review the cases of the men the Task Force originally saw as unfit for transfer or trial.

Because of the delays in implementing the president's commitment to close the prison at Guantanamo, detainees have begun losing hope. In a speech to Congress in spring 2013, Gen. John Kelly of U.S. Southern Command conceded that detainees were "devastated" that Obama had "backed off … of closing the facility." A hunger strike broke out . By the summer of 2013, more than 100 detainees were on strike. In December of last year, the Defense Department stopped releasing figures on the hunger strike, in an effort to undermine the protest.

Without addressing this blight, history will interpret Obama's legacy on Guantanamo as one that reinforced — not repudiated — indefinite detention without charge or trial. The president could and should release those detainees held at Guantanamo who have never been charged with a crime.

The only real impediment the PRBs suffer is the administration's failure to prioritize them. And if Obama is to make good on his promise to shutter the Guantanamo facility he must, at the very least, get the PRBs moving again.