A kapo was a prisoner in the Holocaust camps who was assigned by the SS to supervise other prisoners or carry out administrative tasks and given special privileges. Related groups included the "Jewish Ghetto Police" or "Jewish Police Service" in the Holocaust ghettos.
Even politically correct sources state that the kapos and the Jewish Ghetto Police committed many crimes. Initially, in the postwar period, there were several trials involving former kapos, but they eventually came to be perceived as victims themselves. Wikipedia states that Israel’s Supreme Court aimed to stop trials against kapos and other claimed collaborators.
Hirsch Barenblat, a head of the Jewish Ghetto Police and later the conductor of the Israel National Opera, was found guilty in Israel of ensuring that Jews selected for the "death camps" did not escape. Barenblat was initially sentenced to five years in prison. In 1964, having served three months of the sentence, Barenblat was freed and Israel’s Supreme Court quashed his conviction.
Non-prisoner camp personnel, in contrast, continues to be hunted and convicted by courts, with more recently simply being posted at a camp being enough for conviction. See also John Demjanjuk and Helmut Oberlander.
Similarly, non-Jewish claimed collaborators have continued to be hunted and convicted.
The kapos sometimes numbered as high as 10% of the inmates. One effect of this was that the number of non-prisoner staff who had direct contact with the prisoners was very low in comparison to prisons today. However, politically correct Holocaust fictional descriptions often give the impression that all camp supervisors were (cruel) Germans, or, if kapos are depicted, they are often depicted as innocent bystanders.