How to report guaranteed illegal paper plates on a vehicle used to skirt registering and insurance?

So I know of at least two vehicles at my apartment complex that have illegal plates. I know for a fact they are illegal because they have magically "renewed" and been reset three times so far this year.

For those that don't know, paper plates are NOT allowed to be renewed. Not only does this mean they are being cheap, but they also don't have insurance as you have to have a registered vehicle to insure it. This means they are putting other drivers at risk by driving around with no insurance and if they hit somebody the other party is screwed. They are frequently drunk drivers too as I often see them stumbling out of their trucks and dropping beer bottles out the window. They are an accident waiting to happen.

What I am not clear on is where do I go to report these vehicles? County Tax office? Police? Somebody else?