Prosecutors pursing a perjury conviction against baseball star Roger Clemens acknowledge they made a critical error that ultimately doomed their high-profile trial but asked a judge for another chance to convict the pitching standout of lying about using performance-enhancing drugs.  Read more after the jump.

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The U.S. attorney’s office for the District of Columbia filed arguments Friday disputing Clemens’ position that a second trial would violate his constitutional protection against double jeopardy by making him face the same charges twice. The filing is the prosecutors’ first public admission of fault in the mistrial and first explanation of what went wrong.

The prosecutors wrote it was their duty to make sure that evidence was not included in their exhibits. “The government accepts responsibility for its oversight, and regrets the burdens that error has placed on this court and defendant,” they wrote, but argued the mistake was due to the press of other trial matters and was not intentional.

They said it was an oversight that they showed jurors evidence that U.S. District Judge Reggie Walton had ruled inadmissible – evidence that the defendant’s teammate told his wife that Clemens had admitted using performance-enhancing drugs.

Clemens had argued the showing of the evidence was a deliberate ploy to invoke a mistrial because the prosecutors’ case was going badly. But the prosecutors say their case remains strong and Clemens wants to “gain an unwarranted windfall from this inadvertent error.”

That’s an important point for the prosecutors to make to the judge, who has scheduled a Sept. 2 hearing on the retrial debate. Normally, when a defendant requests a mistrial, a second trial is not considered double jeopardy. The exception would be when the judge finds prosecutors intentionally provoked a mistrial.

But the prosecutors pointed out the sudden ending to Clemens’ trial came only on the second day of evidence in what was supposed to be a four- to six-week case. It came before prosecutors called crucial witnesses such as Brian McNamee, the pitcher’s longtime trainer, who said he injected Clemens with steroids and human growth hormone, or showed their key physical evidence – needles that McNamee said he used to inject Clemens and which the prosecutors said contained Clemens’ DNA and traces of the drugs.

The defense planned to dispute both vigorously, arguing that McNamee is a habitual liar who fabricated the evidence to blackmail his former boss. But jurors only had hints of that dispute in opening arguments and had seen no evidence of it yet.

“It is impossible to credibly assert that the government had a motive for derailing defendant’s prosecution because it believed the case was going badly when the case was barely going,” the prosecutors said.

Clemens has steadfastly denied using performance-enhancing drugs during a standout 24-season career in which he broke multiple records pitching for the Boston Red Sox, Toronto Blue Jays, New York Yankees and Houston Astros. Clemens was the most prominent player accused of using drugs in a December 2007 investigative report to Major League Baseball led by former Sen. George Mitchell. Clemens went before a House committee in February 2008 to fight the allegations. He is charged with lying under oath by telling lawmakers he never used the drugs.

The quick end to his trial came when prosecutors were showing jurors a video of Clemens’ testimony. In the video, Rep. Elijah Cummings, D-Md., was questioning Clemens and pointed out that his good friend and teammate Andy Pettitte says Clemens admitted using human growth hormone in a private conversation in 1999 or 2000. Clemens responded that Pettitte “misheard” or “misremembered” their conversation. But Cummings said Pettitte’s wife, Laura, has given lawmakers an affidavit saying that her husband told her about the conversation with Clemens at the time it happened.

Walton had ruled the day before the trial began that Laura Pettitte’s comments were inadmissible hearsay because she didn’t speak to Clemens directly. When prosecutors aired the video, Walton sent jurors out of the courtroom and scolded the government attorneys for a move that a “first-year law student” would have known to avoid. Clemens attorney asked for a mistrial and Walton granted the motion, saying Clemens couldn’t get a fair trial with a jury that had seen the video.

Prosecutors pointed out that Walton’s ruling on Laura Pettitte’s statement came the day before the trial began, long after their exhibits had been prepared and as they were preoccupied with jury selection, opening statements and other trial matters. But the prosecutors acknowledged they should have redacted their exhibits to comply with Walton’s ruling.

“Unfortunately, neither government counsel additionally focused on whether the substance of Laura Pettitte’s testimony might be embedded in a question of one of defendant’s congressional interlocutors,” said the filing. The prosecutors said the reference to Laura Pettitte “would have been removed had government counsel adequately focused on it.”

Friday’s filing was signed by assistant U.S. attorneys Steven Durham and Daniel Butler, the two prosecutors who conducted the trial, along with their boss, U.S. attorney for the District of Columbia Ronald Machen Jr. and a colleague from the office’s appellate division. That suggests there has been no change in the prosecution team despite the error.

The U.S. attorney’s office declined to answer any questions, noting that Walton has issued a gag order preventing parties from commenting.

In San Francisco, prosecutors have not yet said whether they will attempt to retry home run king Barry Bonds. A mistrial was declared in April after a jury deadlocked on three counts charging Bonds with lying to a grand jury in 2003 when he denied using performance-enhancing drugs and said he allowed only doctors to inject him. Bonds was convicted of one count of obstruction of justice for giving the grand jury an evasive answer, and a hearing is scheduled for Thursday on Bonds’ attempt to set side that conviction.