The U.S. military acknowledged Thursday it held an Afghan man for a month after taking custody of him from a trio of American counterterror vigilantes who have since been arrested on charges of torturing prisoners at a private jail they ran in the Afghan capital.

The American military has tried to distance itself from the group, led by a former American soldier named Jonathan Idema (search), insisting they were freelancers working outside the law. But spokesman Maj. Jon Siepmann acknowledged that the military had received a detainee from Idema's group at Bagram Air Base (search), north of Kabul, on May 3.

Siepmann said Idema had appeared "questionable" the moment he presented the detainee, and that suspicion grew when, one month later, the man turned out not to be the top suspect that Idema had described.

"That doesn't mean at the time that we knew Mr. Idema's full track record or other things he was doing out there," Siepmann said. "This was a person who turned in a person who we believed was on our list of terrorists and we accepted him."

Siepmann did not release the detainee's name or say what crimes he was wanted for.

He suggested that the military was initially taken in by Idema, who officials say had been posing as a U.S. special forces soldier.

Afghan security forces seized Idema, two other Americans and four Afghans on July 5 after freeing eight prisoners from a makeshift jail in Kabul. The arrests came only after international peacekeepers contacted the U.S. military about their own suspicion of Idema's group, which duped the NATO-led force into helping in three raids in late June.

The seven defendants went on trial in Kabul on Wednesday, charged with hostage-taking and torture.