That is perhaps valid, though a counter argument is that in many police states such people are executed instead of imprisoned.

Typically it means the police are an instrument of whomever is controlling the state to keep themselves in power, e.g. per Wikipedia "Police state is a term denoting government that exercises power arbitrarily through the police. (https://en.wikipedia.org/wiki/Police_state).

I also like to define Japan as a police state, a polite one, granted, but policing was done for the convenience of the police, not for "justice" as we at least attempt. I.e. it's more important to close a case than get the real perpetrator, which was made easy by a "judicial" system with a combined "confession" and conviction rate exceeding 99.9% (really). Past tense because citizen jurors of some sort have recently been added to the mix, although I note that the history of that in England suggests it'll be a long time if ever before that becomes anything resembling the common law system.