Jurors in the perjury trial of Roger Clemens will be able to consider Andy Pettitte’s wavering testimony about a conversation he had with Clemens, his former teammate, bout performance-enhancing drugs, a federal judge said Monday.

In one of the most dramatic moments of the trial, now in its fifth week, Pettitte backed away from his initial recollection that Clemens had confided in him about using human growth hormone during a workout at the star pitcher’s home in 1999 or 2000.

Under cross-examination, Pettitte conceded that he might have misunderstood Clemens.

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Pettitte’s uncertainty was a blow to federal prosecutors who were counting on the ballplayer to bolster the testimony of Brian McNamee, a strength coach with a troubled background who is expected to take the stand later Monday.

But Walton’s decision will leave it to jurors to assess which version of Pettitte’s story most accurately reflects what Clemens told him.

“The jury could conclude that what he said on direct and what his recollection was what actually occurred, despite what he said on cross,” Walton said, siding with the government’s argument not to strike the Pettitte’s testimony as defense lawyers had requested.

Clemens is charged with perjury, obstruction of Congress and making false statements when he denied using steroids or human growth hormone during interviews with Congressional investigators and House lawmakers in 2008.

The House Committee on Oversight and Government Reform was investigating the use of performance-enhancing drugs in Major League Baseball following a 2007 report by former senator George Mitchell that named dozens of ballplayers including Clemens.

In another boost to government lawyers, Walton also blocked access to McNamee’s divorce records, which were expected to portray the former trainer in an unflattering light.

McNamee was a source for Mitchell’s report and has said that he injected Clemens with HGH and steroids between 1998 and 2001.

Before jurors entered the courtroom Monday, Walton had a confession to make to prosecutors and defense attorneys: A stickler for the rules, Walton admitted to accidentally giving jurors a pile of magazines that included a Sports Illustrated with an article on the case.

It does not appear that any of the jurors read the piece, he said.

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