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A forensic scientist testified Friday that two cotton balls and a syringe needle allegedly saved after a steroids injection tested positive for Roger Clemens' DNA, a key moment as the government tries to prove the former pitcher used performance-enhancing drugs.

Alan Keel told jurors that the DNA on both cotton ball matches were "unique to one person who has ever lived on the planet" — Clemens. He said that one of the cotton balls had a random match possibility of one in 15.4 trillion for Clemens' DNA, and the other had one in 173 trillion, when comparing to the population of white people in the U.S.

The needle was not as conclusive, because Keel was only able to get a handful of cells. That match was one in 449.

Brian McNamee, Clemens' former strength coach, earlier testified he collected the medical waste after injecting the pitcher with steroids in 2001, and turned them over to federal authorities in 2008. Earlier government witnesses testified that steroids were found on the medical waste.

Clemens is accused of lying to Congress in 2008 when he denied using performance-enhancing drugs.

Prosecutors hope that Clemens' DNA — which helped make him one of the most successful pitchers in baseball history — will help them convict him of a federal crime.

While Keel's testimony was a milestone moment for the government, the defense indicated early on it wouldn't contest that the needle had both steroids and Clemens' DNA on it. But Clemens' lawyer Rusty Hardin said in his opening statement that the defense will contend that McNamee put the steroids in the needle after injecting Clemens and that the coach in fact had used the needle to inject Clemens with vitamin B12. Clemens has maintained for years that he received B12 shots and the local anesthetic lidocaine but not performance-enhancing drugs.

Prosecutor Courtney Saleski tried to pre-empt that by asking Keel if there was any way to "fake this."

Keel said no.

"If this were contrived, I would expect to obtain much more biological material," he said — in other words, it would be hard to fake a sample with such a small amount of biological material on it.

The gauze pad, meanwhile, matched McNamee's DNA, to an even greater probability than Clemens did for the cotton balls. Keel said that the match was 1 in 1.8 quintillion people for white Americans. A quintillion has 18 zeroes in it.

During cross-examination, Clemens lawyer Michael Attanasio tried to suggest the possibility of contamination in the items McNamee saved.

But Keel said that if there were contamination, he would have expected to find McNamee's DNA on the needle. But he found only found Clemens'.

Attanasio suspended his cross-examination for the lunch break and planned to finish it Friday afternoon.

Also Friday, U.S. District Judge Reggie Walton said he would have a hearing on Monday, June 4, to discuss the defense subpoena for the testimony of Rep. Darrell Issa, chairman of the House Oversight and Government Reform Committee. That committee held the congressional hearing that Clemens testified before in 2008. Issa, a California Republican, was not chairman at the time, but he participated in the congressional deposition of Clemens and criticized the panel, then run by Democrats, for having the hearing on steroids in baseball.

Issa and the committee have filed a motion to quash subpoenas for the congressman and for committee documents. They argue the subpoenas are barred by the Constitution's speech or debate clause, which protects elected officials from being questioned in a lawsuit about their legislative work.

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AP Sports Writer Joseph White contributed to this report.

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