Federal prosecutors in Philadelphia are investigating the conduct of a U.S. government lawyer who nearly derailed the death-penalty trial of confessed Al Qaeda conspirator Zacarias Moussaoui by improperly coaching witnesses on their testimony.

The criminal investigation of Carla J. Martin, a lawyer with the federal Transportation Security Administration, was disclosed in recently unsealed transcripts of a closed March 21 hearing in the Moussaoui case.

U.S. District Judge Leonie Brinkema said in the hearing that she had been "advised by the U.S. Attorney's Office that there may very well be a prosecution of her, at least they're looking at the possibility."

Rob Spencer, the lead prosecutor in the Moussaoui case, responded that "the matter has been referred to a prosecutor in the Eastern District of Pennsylvania, and I believe they are handling the matter."

Prosecutors in Alexandria withdrew themselves from the investigation.

Moussaoui's defense lawyers have said Martin should face criminal charges for witness tampering.

Martin's misconduct delayed the Moussaoui trial for a week and almost derailed it completely when it was revealed a week into the trial.

Martin improperly coached seven aviation witnesses on their testimony, urging them to read transcripts of the trial's first day and warning them to be prepared for certain topics on cross-examination. All of this violated a judge's order barring witnesses from exposure to trial proceedings, for fear that they would shape their testimony based on what they had heard.

Martin was apparently concerned that prosecutors overstated the Federal Aviation Administration's ability to prevent the Sept. 11 attacks and wanted witnesses to be prepared for tough questions on cross-examination.

After Brinkema learned the extent of Martin's misconduct in a special evidentiary hearing, she barred the government from presenting any evidence about aviation security to the jury. She reconsidered after prosecutors said it would gut their case, and allowed the government to present an aviation witness who was not tainted by Martin's misconduct.

Martin has refused to testify about her actions. Her lawyer, Roscoe Howard, has said she will explain herself to Brinkema at the appropriate time.