The judge in the trial for Sept. 11 conspirator Zacarias Moussaoui issued a devastating blow to the prosecution's death penalty case Tuesday, barring key witnesses after she learned a government lawyer had improperly shared information with them.

"I am removing from this case any and all witnesses and evidence dealing with the aviation component," U.S. District Judge Leonie Brinkema said.

"What we have in this case ... is that six witnesses -- two for the government and four potential defense witnesses, were tainted," she said.

Brinkema had rejected a Moussaoui defence request that she dismiss the government's death-penalty bid, but a CTV Newsnet analyst said the judge did the next best thing.

"This prosecution is over at this point," Steven Skurka said Tuesday.

"This really was the heart of this case. And without these witnesses, it can't go forward. That's why the prosecution was fighting so hard -- to not have the judge do what she did."

The witnesses were expected to testify that they would have issued alerts and implemented security measures at airports if Moussaoui had revealed his al Qaeda membership and the true intent of his flight training when he was arrested in August 2001.

Brinkema approved a postponement of the trial until Monday to give prosecutors time to consider whether to appeal her decision.

If prosecutors appeal Brinkema's ruling to the 4th U.S. Circuit Court of Appeals in Richmond, the trial itself could be delayed.

Carla J. Martin, a lawyer for the Transportation Security Administration, had been expected to testify Tuesday, but she invoked her right to an attorney. That attorney, Roscoe Howard, later advised her not to testify.

Trial halted

Brinkema abruptly halted the death penalty trial Monday and ordered the hearing after learning Martin had communicated with seven aviation officials, who were to testify as witnesses, and had them prepared for certain questions on cross-examination.

Martin emailed the upcoming witnesses a transcript of the trial's first day and her analysis of the government's opening statement and of vulnerabilities exposed in the government's case.

Federal rules prohibit trial witnesses from exposure to trial transcripts or from following the case, to guard against their being coached or altering their testimony.

"Whether the witnesses have actually been tainted or not is almost impossible to tell," Brinkema said.

"There are a number of errors so serious that that portion of the government's case has been seriously eroded."

The trial, now in its second week, will decide if Moussaoui will get the death sentence or spend life behind bars.

Moussaoui pleaded guilty last April to conspiring with al Qaeda to fly airplanes into U.S. buildings. However, he denies having anything to do with the Sept. 11 plot, saying he was training for a possible future attack.

The government's debacle in its bid to execute the only man charged in connection with the terrorist attacks that claimed 3,000 lives has also angered the families of the victims of Sept. 11, 2001.

"I felt like my heart had been ripped out. I felt like my husband had been killed again," said Rosemary Dillard, whose husband Eddie was killed when a plane smashed into the Pentagon. "I felt like the government has let me down once again."

With files from The Associated Press