WASHINGTON (AP) — A federal judge has ordered an independent medical review for a Saudi held at the Guantanamo Bay detention center who was 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 has suffered from mental illness since childhood that has worsened at Guantanamo and he should be returned home to Saudi Arabia for treatment. The government opposes repatriation and says he can get sufficient treatment at the U.S. base.

On Friday, U.S. District Judge Rosemary Collyer directed the government to set up a Mixed Medical Commission that would consist of an American military doctor along with two physicians from a neutral third country to determine if he meets the standard of a 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.

The Department of Justice said Monday that it is reviewing the opinion and has not said whether it would appeal.

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

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 brutally interrogated in a way that the Pentagon legal official in charge of the war crimes commissions said amounted to torture. A military review board has repeatedly determined he was a threat to U.S. security and should not be released from the detention center, where he is one of 40 prisoners in custody.