The head of the U.S. Anti-Doping Agency has lobbied the Justice Department to join a whistle-blower lawsuit against cyclist Lance Armstrong filed by his former teammate Floyd Landis.
The Justice Department has not announced whether it will join the case.
The letter accuses Armstrong of committing fraud against the U.S. Postal Service, which sponsored most of his teams when Armstrong used performance-enhancing drugs to win the Tour de France.
USADA chief executive Travis Tygart wrote Attorney General Eric Holder on Jan. 14, saying "fraud and other crimes were committed."
The letter was first reported Thursday by Velonews.com, and The Associated Press independently obtained a copy, the day after Armstrong announced he would not speak under oath with USADA investigators.
USADA officials said Armstrong was concerned about possible legal exposure in pending legal cases.