Awad al-Bandar, one of Saddam's seven co-defendants who testified last month, was cross-examined for a second time over the trial of the Shia before his Revolutionary Court in 1984.
Al-Bandar stood alone in the defendants' pen as the chief judge, Raouf Abdel-Rahman, and prosecutors questioned him.
Saddam was not in the court. A day earlier, the former president was cross-examined by prosecutors for six hours for the first time in the six-month trial.
Prosecutors are seeking to show that al-Bandar's court gave the 148 Shia only a cursory trial on charges that they tried to assassinate Saddam in the town of Dujail in 1982 - and that Saddam approved their death sentences even though many had nothing to do with the shooting attack on him.
Al-Bandar said: "It was a legal and a just court. I was keen to carry out justice and I hoped that the defendants would be found not guilty... May God be my witness, it made us happy whenever a defendant was released."
"If I, as a judge, issue a sentence in accordance with the law, should I be punished?"
But he acknowledged that none of the 148 in the Dujail case was found innocent, saying they had confessed to trying to assassinate Saddam "with instructions from the government of Iran to overthrow the regime in Iraq".
"There were defence lawyers and they were given the chance to present their defence," al-Bandar said. "All the defendants were present in the court. They confessed before me and the ruling was issued. If I, as a judge, issue a sentence in accordance with the law, should I be punished?"
Saddam and the seven former members of his government face possible execution by hanging if found guilty over the crackdown against residents of Dujail after Saddam's motorcade was shot at as it passed through the town in 1982.
Hundreds - including women and children - were imprisoned, some of them saying they were tortured, and 148 people were executed.
The defendants say their actions were a legal response to the assassination attempt. But prosecutors have sought to show that the reprisals went far beyond the actual attackers.
In his testimony on Wednesday, Saddam said he was convinced that the 148 detainees were guilty, but evaded questions about how closely he had looked at the evidence.
Asked if he had read the evidence against the men before referring them for trial, Saddam said: "If the constitution requires the head of state to review documents before referral, then I abided by it."
Pressed by prosecutors on the point, he said: "I have answered."