Key figures in the Clemens trial

Some of the key figures expected at Roger Clemens' trial, scheduled to begin today, on charges he lied about using steroids and human growth hormone:

- Roger Clemens: The standout pitcher maintains he never used performance-enhancing drugs during a 23-season career that ended with ended with 354 wins, 4,672 strikeouts and a record seven Cy Young Awards. But prosecutors say he is lying and broke the law when he made his denials under oath before a congressional committee.

- Brian McNamee: The strength trainer worked out closely with Clemens for a decade, helping mold him into one of the most feared power pitchers in the major leagues even into middle age. McNamee also says he injected Clemens with steroids and human growth hormone and saved the needles, which will be evidence at trial. He's the only person to say he witnessed Clemens using drugs and will be the prosecution's most important witness.

- Andy Pettitte: Clemens' fellow pitcher for the New York Yankees and Houston Astros is another vital prosecution witness because he's the only person besides McNamee who says Clemens acknowledged using drugs, in a private conversation in 1999 or 2000. Clemens has said his former friend is "a very honest fellow" but insists he "misremembers" their conversation.

- Kirk Radomski: The former batboy with the New York Mets has admitted providing drugs to dozens of players and was the primary source behind the 2007 Mitchell Report examining the use of performance-enhancing drugs in Major League Baseball. McNamee says he got the drugs for Clemens from Radomski. And prosecutors say Radomski will testify that McNamee told him that he had saved needles he had used to inject players.

- U.S. District Judge Reggie Walton: The judge is no stranger to high-profile litigation, having presided over the trial of Vice President Dick Cheney's former chief of staff, Scooter Libby. Walton was appointed to the federal bench in 2001 by President George W. Bush after serving on the District of Columbia Superior Court and as an adviser for crime and drug policy to President George H.W. Bush. He also was an athlete - he went to college on a football scholarship and revealed in a recent Clemens hearing that he and Ken Griffey Sr. grew up playing ball together in their hometown of Donora, Pa.

- Rusty Hardin: Clemens' lead attorney has a long list of high-profile clients from his Houston firm, including politicians and many other professional athletes. He persuaded the Supreme Court to overturn a conviction against accounting firm Arthur Andersen and successfully defended the wife of TV evangelist Joel Osteen after a flight attendant said she assaulted her when a spill on her armrest wasn't quickly cleaned up. Hardin has a reputation for winning jurors over with plenty of Southern charm and colorful quips aimed to bring down opponents.

- Michael Attanasio: Clemens hired the San Diego-based former federal prosecutor to address a conflict of interest with Hardin, who also briefly advised Pettitte just before the release of the Mitchell Report. Attanasio will cross-examine Pettitte and has deep familiarity with the issues in this trial. He's the son of a baseball agent and advised the San Diego Padres during the Mitchell Report investigation.

- Assistant U.S. Attorney Steven Durham: The chief of the public corruption unit at the U.S. attorney's office in Washington has directed a wide variety of white-collar prosecutions, including one against Riggs Bank that resulted in the largest criminal fine in the history of the Bank Secrecy Act and another against Siemens AG that was the largest corporate prosecution under the Foreign Corrupt Practices Act. Durham also prosecuted baseball player Miguel Tejada, who pleaded guilty to a misdemeanor of misleading congressional investigators who questioned him about steroids.

- Assistant U.S. Attorney Daniel Butler: He specializes in fraud and public corruption cases and successfully prosecuted two racketeering trials, one involving 10 defendants who robbed six banks with machine guns. The other was the case of "D.C. madam" Deborah Jeane Palfrey, who ran an escort service that catered to high profile clients including Sen. David Vitter, R-La.

- Jose Canseco: The former Major League outfielder wrote a best-selling 2005 book, "Juiced," in which he admitted using steroids and accused most other players of doing so as well. He has said he had suspicions but no proof that Clemens used steroids. One of the accusations against Clemens is that he lied when he said he did not attend a 1998 party at Canseco's Miami home in which they discussed steroids. Canseco also has said Clemens wasn't at the party, but several other attendees said the pitcher was.

- Chuck Knoblauch and Mike Stanton: Clemens' former Yankee teammates are expected to testify about how they got human growth hormone from McNamee. Clemens is fighting to keep such testimony out because he says it will create guilt by association, but prosecutors say it's important to establish McNamee's knowledge of drug use and credibility when Clemens accuses him of lying.

- David Segui and C.J. Nitkowski: The former Major League Baseball players may testify that McNamee told them before the allegations became public that he injected Clemens with drugs or kept the evidence of the injections - evidence that McNamee didn't make up the story in 2007 to save himself from prosecution on drug charges as Clemens claims.

- George Mitchell: Major League Baseball picked the renowned former Maine senator to lead an investigation into the use of performance-enhancing drugs. His explosive 2007 report accused 86 current and former players of using drugs, including Clemens. Clemens' lawyers have indicated they may call Mitchell to testify, presumably about what McNamee and Radomski told him during his investigation.