BAGHDAD, Iraq – A defense witness stunned the court trying Saddam Hussein and fellow regime members yesterday by testifying that nearly two dozen Shiites the defendants are accused of killing are still alive.

The claim by the anonymous witness prompted Chief judge Raouf Abdel-Rahman to order an inquiry.

Defense lawyers said that if the claim was true, the court should review the entire case against Saddam and his seven co-defendants. Saddam and his former intelligence chief, Barzan Ibrahim, stood in court and called for an investigation.

“We heard today a very dangerous thing, which puts the court at a crucial crossroads,” Mr. Ibrahim said.

He even called for American officials – whom he has repeatedly accused of interfering in the trial – to help with the investigation. “We trust the Americans more than Iraqis,” he said.

Saddam and his former regime members are accused of killing and torturing Shiites in a crackdown launched in Dujail after a 1982 assassination attempt on the former leader. Prosecutors say 148 Shiites were sentenced to death for their alleged roles in the assassination attempt, and they all were either hanged or tortured to death.

Saddam and his co-defendants could be hanged if convicted of crimes against humanity.

But the witness, who testified from behind a curtain to protect him from reprisals, said he recently saw 23 of those Shiites who were sentenced to death.

“I’ve eaten with them, I’ve met them,” the witness said. “I can take the chief prosecutor to Dujail and have lunch with them.”

He gave Judge Abdel-Rahman the names of six he claimed are alive.

Chief prosecutor Jaafar al-Moussawi cast doubt on the witness, saying records showed the man was not a resident of Dujail as he claimed.

The development came as the defense said one of its witnesses had been killed and complained that security threats were hampering its case.

“The defense is not free to present its witnesses the way the prosecution is,” one defense lawyer told Judge Abdel-Rahman.

The lawyer said some potential defense witnesses will not appear in court because they are wanted by the American military or Iraqi government. He did not elaborate.

The witness who was killed was not identified in court. But a defense lawyer, Najib al-Nuaimi, told the Associated Press it was a son of defendant Mizhar al-Ruwayyid who testified two weeks ago, Ziyad Mizhar al-Ruwayyid.

Ziyad was shot to death Monday by gunmen in Dujail, and another relative who testified, Mizhar’s uncle, Saleh, was kidnapped, Mr. Nuaimi said. Members of the Shiite Badr Brigade went to the home of another witness and threatened his family members, Mr. Nuaimi said, without identifying the witness.

“There is a big problem in Dujail,” Mr. Nuaimi said. “They are going after any witnesses who are there. There is a lot of fear.”

American and Iraqi leaders hope a fair trial could help Iraq’s Shiites, Sunnis, and Kurds put the atrocities of Saddam’s regime behind them.

Two defense lawyers were killed early in the trial, and a defense attorney accused a spectator Monday of belonging to a Shiite militia that has threatened lawyers. The judge ejected the spectator.

The defense complaints came after Judge Abdel-Rahman chided Saddam’s team for trying to expand its witness list. The judge has shown increasing impatience with witnesses having no direct connection to the case.

Judge Abdel-Rahman also refused a defense request to show DVDs as evidence, telling the lawyers to make a written request.