International Criminal Court (ICC) prosecutions are well publicized and therefore very likely to be tried in the media, which will automatically give them a political slant. There have also been several, such as the ones in Africa, where the defense has used politics in order to try to invalidate the findings of the ICC investigations. Although politics really has no place in a judicial system, with the current system it is unavoidable.
On an international level, having so many concerned parties with different agendas, I believe that it is unrealistic to expect to avoid politicization. One man's criminal is another man's war hero. One man's villain is another man's terrorist. What one nation sees as a flagrant crime, another nation might see as a legal and reasonable course of action. Therefore, I do not think that it's possible to avoid politicization of ICC prosecutions.