A Department of Defense spokesperson confirmed to ABC News that Slahi has been designated for transfer but that his release will not happen until the U.S. negotiates with another country to accept him. The Periodic Review Board posted a document stating simply that they had determined that continued detention of Slahi "is no longer necessary to protect against a continuing significant threat to the security of the United States."
The document also noted "clear indications of a change in the detainee's mindset," which contributed to the decision.
An unclassified detainee profile of Slahi found on the Periodic Review Board website suggests why Slahi was held. The profile, dated February 2016, says he trained at an al-Qaeda camp and "established a broad network of terrorist contacts while living in Germany, Canada, and Mauritania." He was arrested in Senegal in January 2000, moved to Mauritania, but was arrested again in 2001 and was taken to Guantanamo in 2002, according to the profile.
Although Slahi has been cleared for release, it is unclear when he will actually walk free.
“We’re delighted for Mohamedou and his family, but the new chapter in his life won’t start until the Pentagon actually transfers him, and it should begin that process immediately,” Hina Shamsi, one of Slahi’s attorneys and director of the American Civil Liberties Union’s National Security Project, said in a statement. “There are still dozens of other men trapped in the misery that is indefinite detention at Guantánamo. Time is running out for President Obama to fulfill his promise to close Guantánamo and prevent its injustice from tarnishing his legacy.”
The ACLU also said that the government of Mauritania will welcome him back into their country upon his release.
“We are thrilled that the PRB [Periodic Review Board] has cleared our client,” Nancy Hollander, Slahi's attorney, said in a statement. “We will now work toward his quick release and return to the waiting arms of his loving family. This is long overdue.”