WASHINGTON — U.S. military intelligence assessing the threat of nearly 800 men held at Guantanamo in many cases used information from a small group of captives whose accounts now appear to be questionable, according to a McClatchy analysis of a trove of secret documents from the facility.

The allegations and observations of just eight detainees were used to help build cases against some 255 men at Guantanamo — roughly a third of all who passed through the prison. Yet the testimony of some of the eight was later questioned by Guantanamo analysts themselves, and the others were subjected to interrogation tactics that defense attorneys say amounted to torture and compromised the veracity of their information.

Concerns about the quality of the "facts" from the eight men goes to the heart of Guantanamo's "mosaic" approach of piecing together detainees' involvement with insurgent or terrorist groups that usually did not depend on one slam-dunk piece of evidence. Rather, intelligence analysts combined an array of details such as the items in detainees' pants pockets at capture and whether they had confessed to interrogators — American or otherwise.

More than two-thirds of the men and boys at Guantanamo were not captured by U.S. forces. So analysts were often left to weave together the stories told by detainees, the context of where and how they were initially scooped up, the information passed on by interrogators at other U.S. detention sites and, crucially, the testimony of fellow detainees at Guantanamo.

At Guantanamo, the captives were aware that some prisoners were providing a pipeline of information to interrogators — either to justify their continued detention or for use in potential prosecutions before military commissions.

"I heard there was another detainee talking about me," former Briton detainee Feroz Abassi said in a recent interview with McClatchy. "I thought, let them talk. They're only going to corroborate my story."

After being held at Guantanamo for more than three years, Abassi was released in a diplomatic deal in January 2005 at age 25. He now works as a caseworker at the London-based detainee activist group Cageprisoners.

Abassi said it later became apparent that some informants were "straying away from the truth, trying to save themselves. They crack and they think it helps them to point fingers. But they only dig a hole for themselves."

That appears to have been the case for Mohammed Basardah, a self-described one-time jihadist whose information was used in assessments for at least 131 detainees. In some instances, he accused fellow detainees of training at militant camps or taking part in the fighting in Afghanistan against the United States and its allies in late 2001.

Other times, intelligence analysts simply inserted a sliver of a quote from Basardah about the guilt of everyone caught at Tora Bora — the rugged mountain region where Osama bin Laden and members of his inner circle fled following the Sept. 11, 2001 attacks — as a sort of blanket truism.

The Yemeni's testimony was included despite worries highlighted in a 2008 Guantanamo intelligence assessment that his "first-hand knowledge in reporting remains in question" and a remark that many of fellow prison camp captives seemed "willing to reveal self-incriminating information to him."