The U.S. government has, in a seemingly rare admission of intelligence failing, stated publicly that its central allegation against a former Guantánamo prisoner turned out to be unreliable and was withdrawn in 2011.

Younous Chekkouri was repatriated to Morocco last month after languishing at the controversial detention camp in Cuba since 2002. He is currently detained in Salé prison, near Rabat, awaiting a decision over his release.

But in a letter to Chekkouri’s lawyers before a court session Thursday, the U.S. Justice Department noted it “withdrew reliance” on “all evidence identifying Mr. Chekkouri with the organization known as Group Islamique Combatant Maroc [sic].”

Known in English as the Moroccan Islamic Combatant Group, the group is designated a terrorist organization by Washington and is said to have supported Al-Qaeda’s war against the West.

Chekkouri has said that information linking him to the group was obtained through torture of him and other prisoners as well as lies told by inmates at Guantánamo who were looking for better treatment at the prison, according to the legal charity Reprieve, which represents him.

“The core of [the U.S.] case against him for years was that he was a founder of this Moroccan group — and, as the government now admits, we knocked that falsehood back years ago,” said Cori Crider, a director at Reprieve and lawyer for Chekkouri.

“The tragedy is that Younous is now potentially going to be charged in a Moroccan process for the self-same false allegation.”

The U.S. acknowledgment comes as Chekkouri and his lawyers prepare for a court date in Morocco that will decide whether he should be released. His attorneys believe he is being held on the basis of that U.S. allegation.

When he was transferred from Guantánamo, where he had been held for more than 13 years, there were diplomatic assurances between Morocco and the U.S., according to Reprieve. Those assurances included that he would not be prosecuted and that he would not be detained for more than 72 hours. Abuse in Moroccan custody is well documented.

The United States’ apparent admission of error is important for other prisoners whose Defense Department files contain factual mistakes. “What it demonstrates is that for years the U.S. claimed Chekkouri was a dangerous man with connections to Osama bin Laden,” said Andy Worthington, an investigative journalist and expert on Guantánamo. “Yet when subjected to scrutiny, these allegations against him evaporated completely. A host of allegations by demonstrably unreliable witnesses have been used by the U.S. in the past to justify the continuing imprisonment of prisoners without any credible basis for their imprisonment.”

Fourteen Moroccans have been held in Guantánamo. All but one — Abdul Latif Nasir — have been transferred.