WASHINGTON -- Roger Clemens' perjury case was declared a mistrial on Thursday by Judge Reggie Walton after the government introduced evidence before the jury that Walton had ruled was not admissible.

"[Clemens] is entitled to a fair trial and he cannot get it now," Walton said.

Walton scheduled a Sept. 2 hearing to determine whether to hold a new trial, or whether double jeopardy already has attached because witnesses took the stand. Prosecution and defense have deadlines between now and Sept. 2 to submit arguments on the issue.

The inadmissible evidence was an excerpt -- shown on video with a written transcript included on the screen -- from the Feb. 13, 2008, Congressional hearing in which Rep. Elijah Cummings was questioning Clemens and mentioned an affidavit that Laura Pettitte, wife of former pitcher Andy Pettitte, had given about a conversation she and her husband had in 1999 or 2000.

Drug Policy in Baseball

In that conversation, the Pettittes said they discussed how Clemens had told Andy Pettitte that he had used human growth hormone. Walton said that he considered Andy Pettitte's anticipated testimony to be critical to the government's case, but he had ruled that Laura Pettitte's statements were irrelevant and inadmissible.

In a trial that was expected to last 4-6 weeks and had only completed a lengthy process of jury selection two days earlier, Clemens was alleged to have lied to Congress during that hearing before the House Committee on Oversight and Government Reform. For now, the winner of 354 games and a record seven Cy Young Awards still faces charges of perjury, giving false statements and obstruction of Congress for claiming in the hearing and a deposition eight days earlier that he never used performance-enhancing drugs. Former trainer Brian McNamee, who was to be the star government witness in this trial, had testified before Congress that he had injected Clemens with steroids and human growth hormone, keeping medical waste he said proved it.

After Walton's ruling, Clemens left the courthouse with attorney Rusty Hardin and the rest of the defense team, with Hardin saying Clemens would not be addressing the media and that he also would be honoring Walton's gag order, which remains in effect.

"But it's a beautiful day," Hardin said with a big smile.

The Clemens team was surrounded by members of the media while walking away from the courthouse, Clemens at one point stopping and saying, "I'm not talking. Let me walk home now. Thank you." The media continued to follow Clemens and his attorneys for several blocks until they entered an Au Bon Pain café. Along the way, Clemens stopped to sign several autographs and hugged a female fan.

The suprising developments of Thursday morning came on just the second day of testimony, with only the third of 45 witnesses the government said it intended to call on the stand. Congressional staffer Phil Barnett was testifying, first about the Feb. 5, 2008, deposition of Clemens in which he asked questions on behalf of the committee's then-chairman, Henry Waxman (D-Calif.), and then about the hearing itself. When the testimony turned to the hearing, video excerpts of Clemens' testimony were played on a video screen.

Once the excerpt involving Laura Pettitte appeared before the jury, Walton stopped the proceedings and called the attorneys to the bench before calling a break. After the break, with the jury still out of the courtroom, Hardin stepped to the podium.

"Reluctantly we're going to have to move for a mistrial because of the prejudicial nature [of showing the Laura Pettitte portion of the hearing]," Hardin said.

After severely admonishing Assistant U.S. Attorney Steven Durham for not redacting that portion of the hearing from what was played in court, Walton made it clear he had to seriously consider the defense's motion.

"I don't see how I unring the bell," Walton told attorneys before calling for another break to consult with a colleague.

When the lawyers and Walton were discussing what to do about the situation, Walton said it was the government's responsibility to redact the portion of the Congressional hearing, and that government counsel should have been more cautious.

"I thought I had made it perfectly clear that absent something else happening in this trial, that testimony was going to be irrelevant," Walton said.

Walton had ruled that Laura Pettitte's statements were inadmissible unless the defense attacked Andy Pettitte's credibility on the stand, which Walton said he believed Hardin had the wisdom to avoid for that very reason. And he was obviously incensed that the government had "clearly run afoul" of his pretrial ruling.

"I think a first-year law student would know that you can't bolster the credibility of one witness with clearly inadmissable evidence," Walton told Durham.

Hardin also argued that during the discussions at the bench, the jury was allowed to continue seeing the rolling transcript at the bottom of the video that was being played, with the screen frozen as Cummings was reading Laura Pettitte's affidavit and the following passage in view:

"'I, Laura Pettitte, do depose and state, in 1999 or 2000, Andy told me he had a conversation with Roger Clemens in which Roger admitted to him using human growth hormones.' Mr. Clemens, once again, I remind you. You are under oath. You have said your conversation with Mr. Pettitte never happened. If that was true, why would Laura Pettitte remember Andy telling her about that ..."

With all that in mind, Walton left the courtroom for a break that lasted more than a half-hour to consider his options. In the courtroom, he said several times that he considered Andy Pettitte's testimony -- in which he was expected to say, as he did in a deposition at Congress, that Clemens had told him he'd used human growth hormone -- was critical to the government's case. But having not only the introduction of Laura Pettitte's affidavit but also Rep. Cummings' assertions that Pettitte was considered "one of the most honest people in baseball" was prejudicial because it bolstered Pettitte's credibility before he even testified before the jury.

Walton first returned to the courtroom to inform attorneys that he had decided to declare a mistrial, and then he brought the jurors in to inform them. The 12 jurors and four alternates had been selected during a four-day process of screening that included 54 prospective jurors being individually interviewed based on their responses to an 81-point questionnaire Walton read through with them.

"Ladies and gentlemen, we have taken about a week out of your life, and we have spent a lot of your taxpayer money to reach this point," Walton told the panel, which included 13 women and three men. "There are rules that we play by. Those rules are designed to ensure everyone in this courthouse gets a fair shake. That's particularly true when a man's liberty is at stake. ... I have no other alternative, despite the tremendous loss of time and effort and money, to terminate these proceedings. I apologize for what has transpired. I thank you for your time."