On the same day that jury selection began in the perjury case against former pitching star Roger Clemens, U.S. District Judge Reggie Walton issued a ruling restricting the ability of federal prosecutors to use certain witness statements at trial.

Walton interrupted opening statements on July 13 when a prosecutor, Steven Durham, ran afoul of that court order. The next day, Walton hastily declared a mistrial after prosecutors, for a second time, aired evidence the judge deemed inappropriate. A video contained information Walton said was not allowed.

The sudden collapse of the prosecution was an embarrassment for the government, and observers were left wondering how the prosecution team could slip up in a case that has consumed significant resources and generated national scrutiny. “Something like this should never happen,” said SNR Denton partner Glenn Colton, who leads the firm’s U.S. white-collar and government investigations practice. “In a high-profile case or not, prosecutors need to be vigilant, going over evidence to make sure it’s proper and admissible. This strikes me as a substantial lack of diligence and care.”

Whatever the reason, several former prosecutors were unanimous in doubting the Clemens prosecution team tried to game the system and sneak something past Walton. Still, the government’s blunder and the extensive publicity about inadmissible evidence could make it harder for Walton to pick a second jury, if the U.S. Attorney’s Office for the District of Columbia decides — and is allowed — to try Clemens again on perjury and other charges, said several white-collar defense lawyers who are following the case.

“The carelessness is astonishing,” Wash­ington-based Jones Day partner Henry Asbill said. “If Judge Walton thought it was purposeful and in violation of his order, he may not let them retry the case.”

The U.S. attorney’s office, citing Wal­ton’s gag order, declined to comment on the mistrial. Prosecutors said in court on July 14 that the presentation of the disputed evidence was inadvertent, according to news reports.

Walton said Clemens’ defense attorneys, Russell “Rusty” Hardin Jr. of Hous­ton and Michael Attanasio of Cooley’s San Diego office, have until July 29 to file court papers addressing whether double jeopardy prohibits a retrial. The judge scheduled a motion hearing for Sept. 2. Clemens faces 30 years in prison for charges he lied to Congress about never using performance-enhancing drugs.

In the pretrial ruling at issue, Walton on July 6 forbade the prosecution team, including Durham, chief of the U.S. ­attorney’s office public corruption unit, from telling jurors about two conversations former Clemens teammate Andy Pettitte and his wife, Laura, had about Clemens and drugs. Walton said in the order that prosecutors could be allowed to introduce Laura Pettitte’s testimony only as rebuttal evidence.

Andy Pettitte’s credibility is central to the government’s case against Clemens, and Laura Pettitte’s testimony bolsters the former pitching star’s claim that he and Clemens spoke about performance-enhancing drugs. Clemens testified in 2008 in Congress that Pettitte is not remembering the conversation correctly.

“Nobody’s on trial here for a ­mistake, confusion, neglect or one slip of the tongue,” Durham said in his opening statement. The prosecution, he said, is built on 15 false or misleading statements Clemens made to Congress. “We must prove at least one,” Durham told jurors. “We intend to prove them all.”

The prosecution’s first witnesses were Charles Johnson, who retired in 2004 as the House parliamentarian, and Phil Barnett, minority staff director for the House Committee on Energy and Commerce. Barnett was the House staffer who deposed Clemens in early 2008.

In court last week, prosecutors played for jurors a video of Clemens’ congressional testimony in February 2008 in which Rep. Elijah Cummings (D-Md.) brought up a three-paragraph affidavit in which Laura Pettitte noted the conversations she and her husband had about Clemens.

Walton, according to published reports, immediately stopped the trial to confer with the lawyers. Clemens’ defense team had earlier urged Walton to prohibit Laura Pettitte’s testimony, calling it hearsay.

“Mr. Clemens and Mrs. Pettitte never discussed human growth hormone or anabolic steroids themselves, and the defense is not aware of any other relevant, admissible evidence capable of being offered through Mrs. Pettitte at trial,” Clemens’ attorneys said in court papers filed in June. “Testimony regarding Mrs. Pettitte’s second-hand conversations regarding Mr. Clemens is classic hearsay to which no exception appears to apply.”

In declaring a mistrial, Walton said the government’s conduct “troubled” him. “We’ve spent a lot of money to reach this point,” Walton said, according to The New York Times. “Government counsel should have been more cautious about what was presented so we are not in this situation.”

Walton’s rebuke came one day after he told jurors to disregard a statement Durham made during his opening remarks. Durham was speaking about several potential government witnesses — including Pettitte and other baseball players — and their self-admitted use of performance-enhancing drugs.

Colton said Walton could be leaning toward terminating the Clemens case outright based on the speed he moved to declare a mistrial. The judge’s “rulings are designed to protect the rights of the defendant, and the government did not do that here,” Colton said.

Mike Scarcella can be contacted at mscarcella@alm.com.