WASHINGTON (AP) — A federal judge has ordered that an independent medical panel conduct a review of the mental health of a Saudi prisoner at the Guantanamo Bay detention center who has been accused of trying to enter the U.S. to be the 20th hijacker in the Sept. 11 terrorist attacks.

Mohammed al-Qahtani has been held at Guantanamo for 18 years but never charged because a Pentagon legal official determined he had been tortured at the U.S. base in Cuba.

Lawyers for al-Qahtani say he has suffered from mental illness, including schizophrenia, since childhood and should be returned home to Saudi Arabia for psychiatric confinement and treatment. The government opposes repatriation and says he can be treated at Guantanamo.

On Friday, U.S. District Judge Rosemary Collyer directed the government to set up a Mixed Medical Commission. It would consist of an American military doctor along with two physicians from a neutral third country to determine if his condition meets the standard for required medical repatriation according to Army regulations governing the treatment of prisoners of war under the Geneva Conventions.

It would be the first time such a commission has been ordered at Guantanamo but Shayana Kadidal, an attorney for the 45-year-old prisoner, said a similar process was used for thousands of captured German troops during World War II.

“It is something that is part of the traditional make up of military detention,” Kadidal said. “It’s not something novel. It’s in the Army’s own regs.”

The Department of Justice said Monday that it is reviewing the judge's ruling and has not said whether it would appeal. The Department of Defense did not comment.

Justice Department lawyers argued previously that al-Qahtani is held as an enemy combatant, not a prisoner of war from a defined nation, and does not qualify for the full protection of the Geneva Conventions.

They also said an independent review would be onerous to set up for a single detainee and would inspire others held at Guantanamo to make the same request. They also questioned how the U.S. would determine which countries qualify as “neutral” members of the panel in the war against al-Qaida.

Al-Qahtani was turned away from the country by U.S. immigration officers at the Orlando airport in August 2001 suspicious of the circumstances of his travel. The lead Sept. 11 hijacker, Mohammed Atta, was going to pick him up to take part in the plot, according to previously released documents.

U.S. forces later captured him in Afghanistan and sent him to Guantanamo, where he was subjected to brutal interrogations that the Pentagon legal official in charge of the war crimes commissions said amounted to torture.

The treatment included beatings, exposure to extreme temperatures and noise, sleep deprivation and extended solitary confinement. An FBI official in 2002 observed al-Qahtani speaking to non-existent people, hearing voices and crouching in a corner of his cell while covering himself with a sheet for hours at a time.

A multi-agency board that has reviewed his confinement has repeatedly determined he poses a threat to U.S. security and should not be released from the detention center, where he is one of 40 prisoners in custody.

His lawyers argue that he could not fully participate in the review of his case because of his mental illnesses, which also includes major depression and a possible neurocognitive disorder from a traumatic brain injury caused by a childhood car accident.

They also say his illness raises questions about whether he could have been held legally responsible even if he was charged with attempting to take part in the Sept. 11 attacks or would pose a threat if repatriated.

“We hope that the end point would be that he gets transferred back to basically psychiatric confinement in Saudi Arabia," Kadidal said. "That’s what someone with such severe disease would need and that’s not something that poses a risk to anybody.”