2006 Tour De France
It was cyclist Floyd Landis who originally won the 2006 Tour de France race, doing so in rather spectacular fashion (via a late-stage comeback). But after his win, a urine sample revealed traces of performance enhancing drugs (PED’s) that were up to three times the allowed amount.
After fighting the charges initially, he eventually confessed in 2010, and subsequently became a government informant when authorities began investigating whether revered American cyclist Lance Armstrong had any ties to PED’s. After a decade of denying it, in 2013, Armstrong himself came clean as a result of the investigation and pressure he faced — all because of Landis originally getting caught.