American cyclist Tyler Hamilton, the 2004 Olympic gold medalist, has voluntarily surrendered his medal, after admitting to doping during his cycling career. Hamilton was one of Lance Armstrong’s teammates on the United States Postal Service Team, and he helped Armstrong win the Tours in 1999, 2000, and 2001. Hamilton said in an interview Thursday that he had seen Armstrong inject himself with the banned performance-enhancing drug EPO to win those Tours. Armstrong is the focus of a federal investigation into doping in cycling, and he may be facing charges of fraud, money laundering, corruption, drug trafficking, and wire fraud. One year ago, another teammate, Floyd Landis, said he and Armstrong were part of a systematic doping scheme while racing for the Postal Service team.