The lead prosecutor in the terror case against Zacarias Moussaoui may have known the CIA destroyed tapes of its interrogations of an al-Qaida suspect more than a year before the government acknowledged it to the court, newly unsealed documents indicate.

The documents, which were declassified and released Wednesday by the 4th U.S. Circuit Court of Appeals, detail efforts by Moussaoui's attorneys to send the case back to a lower federal court to find out whether the tapes should have been disclosed and whether they would have influenced his decision to plead guilty.

In a Dec. 18, 2007, letter to the appeals court's chief judge, the Justice Department acknowledged that its lead prosecutor in the case had been informed about the CIA's tapes of al-Qaida lieutenant Abu Zubaydah being interrogated.

The letter said the prosecutor, Robert A. Spencer, may have been told of the tapes' destruction in late February or early March of 2006, just as the U.S. District Court in Alexandria, Va., was beginning its trial on whether Moussaoui would be eligible to face the death penalty.

Spencer, who was one of three prosecutors on the government's team, "does not recall being told this information," U.S. Attorney Chuck Rosenberg wrote in the Dec. 18 letter to 4th U.S. Circuit Chief Judge Karen J. Williams.

Another prosecutor in Rosenberg's office in Virginia's eastern district who was not involved in the case "recalls telling (Spencer) on one occasion," the letter said.

That second, unnamed, prosecutor learned about the videotapes of Zubaydah "in connection with work he performed in a Department of Justice project unrelated to the Moussaoui case," the letter said.

It is unclear what that project was.

Spencer on Wednesday declined comment.

House Judiciary Committee Chairman John Conyers, D-Mich., said the newly released documents underlined the need for an outside investigation of the government's handling of the interrogation tapes.

"This latest disclosure, if true, could amount to a kind of prosecutorial misconduct that undermines our efforts in the administration's 'War on Terror' and the international community's confidence in the American system of justice," Conyers said in a statement. "This is yet another reason that the Justice Department cannot be trusted to police itself and therefore, a special prosecutor must be appointed immediately. The attorney general must be prepared to respond to serious questioning on this issue."

A government official familiar with case said that since the taped interrogations that Spencer knew of only dealt with Zubaydah, the government didn't need to disclose them. Zubaydah already had been declared not relevant to the Moussaoui trial, the official said. The official spoke on condition of anonymity because he was not authorized to speak about the case.

Much of the legal correspondence in the Moussaoui case has been classified and under court seal. The documents released Wednesday offer a glimpse into the court's struggle to determine for sure whether the CIA taped its interrogations of terror suspects.

Moussaoui pleaded guilty in 2005 to conspiring with al-Qaida to hijack aircraft, among other crimes. In a 2006 sentencing trial, a jury concluded that Moussaoui's actions furthered the Sept. 11, 2001, plot in which terrorists flew hijacked airliners into buildings in New York and Washington. But the jury ultimately decided to spare his life and sentence him to life in prison.

The December letter came on the heels of one dated Oct. 25, in which Rosenberg informed the court that the CIA did, in fact, possess videotaped interrogations of enemy combatants. During Moussaoui's sentencing trial, prosecutors told U.S. District Judge Leonie M. Brinkema they did not possess tapes Moussaoui's lawyers were seeking.

The tapes at issue in that letter are not the same ones that were destroyed by the CIA in 2005 and prosecutors assured the judge that they were not related to the Sept. 11, 2001, attacks or the Moussaoui case.

The Justice Department has opened a criminal investigation into the CIA's videotapes, which showed interrogations of Zubaydah and another top al-Qaida leader. They were destroyed, in part, to protect the identities of the government questioners at a time the Justice Department was debating whether the tactics used during the interrogations — which are believed to have included waterboarding — were illegal.

In a written response to the December letter, Moussaoui's attorneys asked the appeals judges to send the case back to the lower federal court that "is in the best position to determine what actually happened and its relevance."

"The timing is important here," Moussaoui attorneys Justin S. Antonipillai and Barbara Hartung wrote in their Dec. 26 response. "The fact that any prosecutor in the same office knew about the existence and destruction of these tapes is surely important evidence."

The appeals court recently rejected the attorneys' request to return the case to the lower court.

Beginning in 2003, attorneys for Moussaoui began seeking videotapes of interrogations they believed might help them show he wasn't a part of the 9/11 attacks. Brinkema on Nov. 3, 2005, asked for confirmation of whether the government "has video or audio tapes of these interrogations" and then named specific ones.

Eleven days later, the government denied it had video or audio tapes of those specific interrogations.

Despite the lapse in disclosure, the government maintains that none of the interrogations related directly to the Sept. 11, 2001, attacks or the Moussaoui case.

Prosecutors also say the issue is moot since a jury failed to impose the death penalty in the case.