“I think that a first-year law student would know that you can’t bolster the credibility of one witness with clearly inadmissible evidence,” the judge said as he raised his voice.

Hardin — who estimated that Laura Pettitte’s testimony remained on the video screen for two to three minutes while the jury looked on — told the judge that the prosecutors’ defiance of last week’s ruling should be enough for a mistrial.

But the prosecution’s mistake was not the first time it had raised the judge’s ire by mentioning or using inadmissible evidence. Walton pointed out it also had gone against his orders during its opening statement Wednesday, during which Durham mentioned that Pettitte and two of Clemens’s other former teammates had used human growth hormone. In a pretrial hearing, Walton had said he would likely not allow the drug use of other players to be mentioned because Clemens could suffer from guilt by association.

Walton told the jurors to disregard Durham’s comments about the players. But on Thursday, he said he could not “un-ring the bell” of Laura Pettitte’s comments being played for jurors.

“I think Mr. Pettitte’s testimony is going to be critical as to whether this man goes to prison,” Walton said, adding that any testimony or evidence that placed Pettitte into a good light — like Cummings’s comments or Laura Pettitte’s testimony — would pose a huge problem for Clemens and his defense.

So, before letting the jurors go, Walton told them that he had decided, sadly, to end the trial because it would be “difficult if not impossible” for Clemens to be judged fairly after the government’s error. Artur Davis, a former federal prosecutor and former United States representative from Alabama, said that the swift decision revealed Walton’s underlying opinion of the case.

“The judge could have just admonished the prosecution and embarrassed them enough to undermine their credibility with the jury, but he purposely chose not to do that,” Davis said. “For him to take the very extreme step of stopping the trial says he was fundamentally skeptical of the case.”