In my story, the protagonist wants revenge on the villains and manipulates members of the police force, to wanting revenge on the villain for the death of an officer, who was killed by accident, but he makes the police make the crime seem much more brutal, sending a dark message, thereby getting friends of the dead cop, out for blood. He manipulates the police force members into forming a vengeful mob to after the villains and kill them. However, how much development would these police characters need? The theme of the story is how wanting justice brings out the worst, in the MC, to the point where me is manipulating members of the system to become his pawns, since the system failed him. I was told by a couple of people that they do not like the cops coming in, in the third act, because they have had no prior development before, accept for the main one on the case, and they are just merely plot device characters. I see what they mean, but is I think they are more theme device characters. The theme being what I said before. So is it wrong for a group of minor supporting characters to be nothing more than theme device characters to get the theme across? Or do these characters need more development in the story, in order for the reader to feel and justify their manipulated actions and descent? It's just I want to cut down and make the story shorter, and not longer, so I do not want to devote more time to them, than mostly the third act. But do I have to, in this case? Since I am writing a screenplay, I tend to use movies as examples? In the movie M (1931), the mafia wanted to locate a serial killer and kill him, so they use a group of homeless people to help out with the hunt. But the homeless people are not given any prior development time before that. So can I them as theme driven characters like that, or is my situation different?