Another way to describe the role of a 'kapo', but not WW2

I'm looking for a way to describe a role similar to a concentration camp kapo, but outside the context of WW2 concentration camps. I need a generalized term that would work for any time-period.

The inference I want is a person with a criminal background (a 'common thug') who benefits through harassing/controlling his own minority group, enabled by a sovereign authority. The type of person who should be in jail (sociopath), but has authority or immunity to justice because of the current power structure.

It does not need to be prison-related, but probably an extreme disparity between the minority group and the sovereign authority: company towns, Apartheid, a military occupation, religious oppression, refugees, or similar – especially where the person's status is unearned, and their actions are a betrayal against the minority group.

It does not need to be a single word. It might be a pejorative, coming from the point-of-view of the people being harassed.

In the civilian prison system, this person can be called a trusty.

trusty
NOUN

A prisoner who is given special privileges or responsibilities in return for good behavior.

There had been a riot over in C Block at breakfast time, and one of the trusties, suspected of grassing, had been doused in hot fat, and set afire.