Andy Pettitte leaves Federal Court in Washington. (May 2, 2012)

Andy Pettitte leaves Federal Court in Washington. (May 2, 2012) Credit: AP

WASHINGTON -- Trainer Brian McNamee testified in the Roger Clemens perjury trial Monday that he was the source for human growth hormone used by Yankees pitcher Andy Pettitte in 2002 -- potentially damaging testimony to Clemens that defense attorneys had fought to keep away from jurors.

McNamee, who has said he injected Clemens with steroids and HGH in 1998, 2000 and 2001, testified that he also provided HGH to former Yankees infielder Chuck Knoblauch in 2001 and referred former Yankees pitcher Mike Stanton to steroid dealer Kirk Radomski.

McNamee also testified he was present when Pettitte, Knoblauch and Stanton used HGH, and that he believes one of the needles he saved in a crushed beer can in 2001 as evidence was from an HGH injection of Knoblauch.

McNamee revealed his ties to the other players for the first time to jurors as Assistant U.S. Attorney Daniel Butler sought to undo the damage inflicted on him, the government's most important witness, during his often contentious cross-examination last week by Clemens' attorney Rusty Hardin.

The testimony was allowed after U.S. District Judge Reggie Walton, who had barred it, agreed with prosecutors that Hardin had opened the door by suggesting the government had specifically targeted Clemens in its steroid probe.

But Walton instructed the jury that testimony by McNamee was only to be used by them in terms of evaluating McNamee's credibility.

"You cannot infer Mr. Clemens' guilt," because McNamee says he injected other players with performance-enhancing drugs, Walton said.

Also Monday, Alexander Lowrey testified under government questioning about a photograph of him as an 11-year old with Clemens in 1998 at the Florida home of Toronto Blue Jays teammate Jose Canseco, an admitted steroid user.

The photo shows Clemens in the water with Lowrey sitting on the swimming pool's edge. Lowrey, 25, said he arrived between noon and 1 p.m., went on a tour of the house, played Wiffle ball and went swimming with a group of kids that included Clemens' son Koby. Lowrey said he twice saw Clemens before finally requesting a photo with him.

Under Hardin's questioning, Lowrey said he "guesstimated" when he arrived and left, and remembers only that it was in 1998. Lowrey also agreed he saw no team buses at Canseco's house and did not recognize any other ballplayers there.

Clemens denies he was at the party at the same time as McNamee.

McNamee testified that he saw Clemens there talking with Canseco and an unidentified man, and that days later Clemens asked him to inject him with steroids for the first time.Clemens faces perjury charges for allegedly lying to Congress in denying McNamee's allegations that he had Clemens with performance-enhancing drugs.

McNamee left the witness stand yesterday after a total of about 26 hours of testimony over six days.

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