Following the September 11, 2001, attacks, the judge who is now President Bush's nominee for attorney general, Michael Mukasey, allowed prosecutors to keep a man behind bars for 10 months without any criminal charges being filed against him. The man, Hussein al-Attas, a roommate of the so-called "20th hijacker," Zacarias Moussaoui, is the third person whose detention Judge Mukasey is known to have supervised during the investigation into the terrorist attacks.

Attas was one of at least 70 men jailed on the basis of material witness warrants during the investigation. Such warrants permit the jailing of crime witnesses to ensure they don't flee before testifying. Civil rights lawyers have criticized their use as an end run around the prohibition against jailing suspects without charges or sufficient probable cause. The 2nd U.S. Circuit Court of Appeals, however, found the use of the warrants after the September 11 attacks to be lawful.

On Capitol Hill, Judge Mukasey's handling of the material witness cases are seen as a window on his views on executive power. Because the cases are sealed, the precise number of material witness cases Judge Mukasey oversaw as a federal judge in Manhattan is unknown. Attas's case differs from the other two material witness cases that have so far been publicly linked to Judge Mukasey because of the length of the detention. The other two detainees  Jose Padilla and Osama Awadallah  were held as material witnesses for about a month before being declared an enemy combatant in Padilla's case or indicted in Mr. Awadallah's case.

After 10 months of detention, much of it in solitary confinement, Attas pleaded guilty in July 2002 for lying to FBI agents. During those 10 months, Attas or his lawyers appeared before Judge Mukasey on at least four occasions to discuss Attas's status, a source with knowledge of the case said. The first conference was on September 20, 2001, the day Judge Mukasey signed the material witness warrant for Attas, the source, who asked not to be identified, said.

Records on Attas's detention remain under seal. One defense lawyer said that at no point did the defense ask Judge Mukasey to release Attas. The reason for not doing so was the expectation that prosecutors would seek an indictment if they were faced with having to release Attas.

"I never raised the issue before the judge," the lawyer, Alexander Eisemann, said. "I didn't think it was in my clients interest to pick a fight with the government over my client's continued detention. The risk was that I was afraid that he would be put on trial next to Moussaoui."

Attas, a Yemeni national who lived with Moussaoui in Norman Okla., in the summer of 2001, had driven his roommate to Eagen, Minn., where Moussaoui tried to enroll in flight school. The two shared a hotel room when Mr. Moussaoui was arrested in August, 2001. In conversations with FBI agents, Attas concealed Moussaoui's identity. The government has never claimed that Attas knew anything of the plot. Mr. Eisemann described Mr. Mukasey's handling of the case as "very principled and fair."

Legal scholars disagree over whether Judge Mukasey should have intervened to prevent an uncharged person from being jailed for so long.

"That an individual was being held for 10 months without charges or evidence that detention was necessary to secure his testimony suggests the need for greater scrutiny of executive action by Judge Mukasey," an expert on habeas corpus law and an attorney at the Brennan Center for Justice, Jonathan Hafetz, said.

Noting that the defense did not seek Attas's release, a former federal prosecutor who is a law professor at Columbia University, Daniel Richman, said: "This was a time of grave national threat and uncertainty and the defendant, for his own reasons, was not pushing this, making it very hard to find any fault with the way the judge handled it."

The government never compelled Attas to testify to a grand jury while he was detained only the basis of the warrant, two sources said. Attas did later give a taped deposition, after his guilty plea, that was played at the death penalty phase of Moussoui's trial. The defense did request that Judge Mukasey ensure that Attas received more regular changes of clothing and a heavier blanket than the single sheet he slept under during winter, according to a letter from April 2002 described by one source who saw it. It is unclear what action, if any, Judge Mukasey took in response.

When Judge Mukasey sentenced Attas in October, 2002, he mentioned only indirectly the fact that Attas was jailed for so long as a material witness. "Attas will be sentenced to time served," Judge Mukasey said, according to a transcript.