Ironically, it's not the first time de la Hoya has opened a can on a cheater. From the Wikipedia:
On September 14, 2002, Oscar fought his nemesis "Ferocious" Fernando Vargas. After fiercely competitive early rounds, Oscar seized control of the latter half of the fight. In round 11, Oscar De la Hoya dropped Fernando Vargas with a left hook. Fernando Vargas got up at the count of nine, but De la Hoya finished him with a barrage of punches forcing the referee to stop the fight at 1:48 of round 11(TKO 11). It was later revealed that Fernando Vargas had tested positive for steroids in his post-fight drug test.