Armed with the government admission of an FBI foul-up over evidence, Oklahoma City bombing co-conspirator Terry Nichols on Monday again urged the U.S. Supreme Court to throw out his life sentence and grant him a new trial.

"The newly discovered fact that the United States withheld concededly discoverable FBI materials casts Mr. Nichols' request ... in a much more favorable light," his lawyers wrote in court papers filed over the weekend and released Monday.

The Supreme Court last month turned down without comment Nichols' request for a new trial for his role in the 1995 terror-bombing that killed 168 people.

On Thursday the Justice Department revealed that more than 3,000 documents were not turned over to lawyers for Nichols and convicted mass murderer Timothy McVeigh. Attorney General John Ashcroft delayed McVeigh's scheduled execution as a result, and now Nichols is asking the court to reconsider his earlier request.

Nichols' lawyers said the revelation about FBI mishandling bolsters their argument that the trial was unfair and that a federal judge essentially took the prosecution team's word that the material was not relevant. The court should have conducted more investigation, Nichols' lawyers claimed.

Some of the documents apparently concern the FBI's search for a possible "John Doe No. 2," another suspect in the bombing, tying in to Nichols' claims that prosecutors exaggerated his role in the bombing.

"The identity of Mr. McVeigh's primary co-conspirator, John Doe No. 2, was a key issue in Mr. Nichols' trial defense and the withheld [documents] regarding the identity of that person went to the heart of," Nichols' request for reconsideration, his lawyers wrote.

At trial, Nichols claimed that John Doe No. 2 was real, and that his existence shed doubt on Nichols' role. Prosecutors claimed that there never was a John Doe No. 2, and that Nichols and McVeigh worked together.

"To a defense lawyer, John Doe No. 2 materials are a fertile source of exculpatory" material that should have been turned over, Nichols' lawyers wrote.

There was no immediate word from the court on whether the documents issue will affect Nichols' case.

Nichols was sentenced in 1997 after he was found guilty in a federal trial of involuntary manslaughter and conspiracy for his role in the April 19, 1995, bombing of the Alfred P. Murrah Federal Building. He was acquitted on federal charges of first- and second-degree murder.

McVeigh was sentenced to death for first-degree murder and other crimes in connection with the bombing after his federal conviction.

The case is Nichols v. United States, 00-8900.

The Associated Press contributed to this report