Is there any case in history where the leaders/officials of the winning country have been punished for war crimes? In most cases I can find of war crimes, the officials/leaders of the losing country are punished for war crime. Is it that the winning country rarely do any war crime or they are able to influence the authorities in their favour?
I will assume you are looking for examples of someone of the victorious nation being punished by an international tribunal, not just by their own country's courts (because, as T.E.D. pointed out, there are many examples of that). It's rare, but it does happen. For example, Ante Gotovina, a key leader in Croatia's victorious military campaign in 1995, was later sentenced to 24 years in prison by an international court, and served some of that time (including several years being held pending trial, which further preceded by 4 years in hiding following his 2001 indictment) before the conviction was later overturned on appeal.
Never. Winning countries have never been punished for war crimes. But Losing countries have never been either.
People of countries are convinced and punished for war crimes. High ranking officers of winning countries are rarely convinced of war crimes (can't think of an example), while it was often the case for some losing countries such as Japan or Germany.
Still, soldiers of winning countries have often been convinced of war crimes, and sometimes executed. Especially, whatever the army, and except for mass events (such as Nankin's rapes), soldiers convicted of rape are often punished as a war crime.