Prosecutors to present DNA in Roger Clemens trial WASHINGTON (Reuters) - Prosecutors were expected to present evidence on Friday of Roger Clemens' DNA on a needle and other items allegedly used to inject the former baseball great with steroids and human growth hormone in a crucial and final phase of their argument. Alan Keel, a DNA expert for Forensic Science Associates in California, was set to take the stand in U.S. District Court in Washington after testifying on Thursday that he was asked to analyze items related to the Clemens trial. If Keel makes a DNA connection between Clemens and items already tested for steroids, the testimony could be critical for the government, which is charging that the former pitching ace lied under oath to a congressional panel in 2008 when he denied using performance-enhancing drugs. The crux of the government's argument has been a batch of medical waste turned in to authorities in 2008 by Brian McNamee, Clemens' former strength and conditioning trainer. McNamee said the waste came from an alleged injection of anabolic steroids he gave to Clemens in August 2001. On Thursday two forensic analysts said they had found steroids on the items, some of which included needles, gauze, and a broken steroid vial that had been stuffed into a Miller Lite beer can. Clemens' attorneys have already indicated they will argue that there is no way to tell how steroids got onto items connected to the pitcher. They countered on Thursday that someone may have dripped steroids over the medical items and that chemicals in the batch of evidence could have mixed together, making it hard to tell whether steroids were on items connected to Clemens. McNamee admitted last week that some of the medical waste was from other players. Anthony Corso, a friend and a client of McNamee's in New York, is another witness the government may call on Friday. Between 2002 and 2004, McNamee allegedly told Corso that Clemens used human growth hormone "regularly" and that McNamee had saved evidence from 2001, according to a court document. McNamee says he injected Clemens with steroids and human growth hormones from 1998 to 2001 and held onto used needles and other items to allay his wife's concerns that he would be the fall guy if the drug usage were discovered. Testimony on Thursday from former Major League Baseball player David Segui bolstered McNamee's claim. The former first baseman who had trained with McNamee in Toronto said McNamee told him over the phone in 2001 that his relationship with Clemens was straining his marriage and that he had kept "darts," slang for needles, to "get her off his back." Clemens, a seven-time winner of the Cy Young Award as best pitcher in his league, has said McNamee injected him with shots of vitamin B12 and the anesthetic lidocaine instead of performance-enhancing drugs.