Lance Armstrong doping case includes Floyd Landis emails and Tyler Hamilton interview

(CBS/AP) AUSTIN, Texas - Lance Armstrong's legal team says Floyd Landis and Tyler Hamilton, former Armstrong teammates who have admitted using performance-enhancing drugs, are part of the U.S. Anti-Doping Agency's efforts to prove the cyclist doped during his record-setting career.

A letter sent from Armstrong's attorneys to USADA on Wednesday said the agency's alleged evidence against Armstrong includes previously disclosed Landis emails and Hamilton's 2011 interview with "60 Minutes." Both men accused Armstrong of doping.

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Armstrong says he's innocent and stresses that he's passed more than 500 drugs tests. USADA has said at least 10 former Armstrong teammates and associates will testify against him. The agency has said it would keep their names confidential to protect them from intimidation.

The letter was the first mention of specific names behind the allegations that Armstrong cheated while winning the Tour de France every year from 1999-2005.

In 2010, Landis wrote an email to USA Cycling chief Steve Johnson alleging he participated with Armstrong in a complex doping scheme when they were teammates. Hamilton's interview with "60 Minutes" aired in May 2011 (watch interview at left) during a federal criminal investigation into doping allegations against Armstrong. The two-year probe ended in February with no charges filed.

USADA's case against Armstrong is now before an agency review board to determine if there's enough evidence to charge him with violations that could result in a lifetime ban from the sport and strip him of his titles. Armstrong, 40, retired from cycling in 2011.

If USADA files charges, the case goes to an arbitration panel to determine Armstrong's guilt.

The latest letter from Armstrong attorney Robert Luskin questioned whether USADA has violated its own rules in presenting evidence and whether the agency's statute of limitations had passed.

Luskin also attacked the credibility of Landis and Hamilton while in urging the USADA review board to recommend dismissing the case.

Landis won the Tour de France in 2006 but was later stripped of his title for steroid use. He first denied doping, then later acknowledged using performance-enhancing drugs during his career.

"Mr. Landis is an admitted, proven liar," Luskin wrote.

Travis Tygart, USADA's chief executive officer, said in a statement his agency was complying with the wishes of the review board.

The board "has expressed concern about the potential for intimidation and retaliation against USADA's witnesses and as part of their review, has asked USADA to only provide additional evidence of doping that is already in the public domain.

"USADA will continue to follow the established procedures that are compliant with federal law and were approved by athletes, the U.S. Olympic Committee, and all Olympic sports organizations."