Probably the cops themselves are the main characters. They are the ones who are in the thick of all the action in 'cop city stories'.
In 'cop city stories', aside from the cops, there might be some recurring characters like the local informants. These informants help the cops with valuable information. They play an important role in the stories as they can provide the crucial leads that the cops need to solve cases. And then there could also be the criminals, who are sort of the antagonists in the stories. Their actions and motives drive the plot as the cops try to stop them.