The Washington Post appears to have broken a significant news story without really knowing it. Here's Perry Bacon, writing about Congressional efforts to move Guantanamo prisoners:

Administration officials say they expect that as many as 40 of the 215 detainees at Guantanamo will be tried in federal court or military commissions. About 90 others have been cleared for repatriation or resettlement in a third country, and about 75 more have been deemed too dangerous to release but cannot be prosecuted because of evidentiary issues and limits on the use of classified material.

75 more... " too dangerous to release but cannot be prosecuted because of evidentiary issues and limits on the use of classified material."   No citation for this figure. 

An administration official said told me that is "too early" to know whether the number will be that high; it depends on whether they can get other countries to accept any more from this group.  But, the official said, it could be "that high."

The Post is fairly definitive. If true, that means that there are 75 so-called "Fifth Category" detainees who might be subject to indefinite detention without trial. President Obama told Americans that this category had to exist:

"Finally, there remains the question of detainees at Guantánamo who cannot be prosecuted yet who pose a clear danger to the American people," Obama said. Among examples he offered: "people who have received extensive explosives training at Al Qaeda training camps, commanded Taliban troops in battle, expressed their allegiance to Osama bin Laden, or otherwise made it clear that they want to kill Americans." He said candidates for indefinite detention without charge would be "people who, in effect, remain at war with the United States."

At the time, administration officials insisted that only a small fraction of detainees would be included in this category. At the time, though, the administration had only begun to review the evidence files and might have simply assumed that the former administration could not have been as totally reckless as it turned out to have been.

Where will be prisoners go? Probably to the prison in Bagram, until the U.S. ends its commitment to fighting in Afghanistan. And then...?