A judge has declared a mistrial in the perjury trial of baseball star Roger Clemens.
U.S. District Judge Reggie Walton said Clemens could not be assured a fair trial after prosecutors showed jurors evidence they were not supposed to see.
Clemens is accused of lying to Congress when he denied using performance-enhancing drugs.
Prosecutors showed the jury a tape Clemens' testimony to Congress, but it included a reference to information that Judge Walton had already deemed inadmissible in court.
One of the chief pieces of evidence against Clemens is testimony of former teammate Andy Pettitte, who said Clemens told him that he used human growth hormone.
Clemens has claimed that Pettitte misheard him.
Pettitte said he also told his wife Laura about the conversation. Prosecutors wanted to call Mrs. Pettitte as a witness to back up her husband's account, but Walton said she couldn't testify because she didn't speak directly to Clemens.
Walton was angered that in the video prosecutors showed the jury, Rep. Elijah Cummings, D-Md., referred to Pettitte's conversation with his wife.
"I think that a first-year law student would know that you can't bolster the credibility of one witness with clearly inadmissible evidence," Walton said.
Walton scheduled a Sept. 2 hearing to determine whether to hold a new trial.
He told jurors he was sorry to have wasted their time.
"There are rules that we play by and those rules are designed to make sure both sides receive a fair trial," Walton told the jury.
He added that such ground rules are critically important when a person's liberty is at stake.