The American cyclist Tyler Hamilton has surrendered his 2004 Olympic gold medal after confessing to doping.
Hamilton won cycling's time-trial at the Athens Olympics and was allowed to keep his medal after testing positive for blood doping because the laboratory accidentally destroyed his B sample by deep freezing it.
However in an interview to be aired by the television program "60 Minutes", Hamilton ended years of denials by admitting to using performance-enhancing drugs, but said he was not alone.
The 40-year-old said he witnessed former team mate Lance Armstrong inject himself with a blood-booster during the 1999 Tour de France, which Armstrong won.
Armstrong, who won the Tour de France seven times, has always denied taking banned substances but has repeatedly had to fend off accusations despite having never failed a drugs test.
His lawyer Mark Fabiani told Reuters on Thursday that Hamilton's accusations about Armstrong were untrue.