I'm not sure on the specifics because I Am Not A Lawyer but civil suits can be filed in federal courts when the dispute explicitly involves federal law (the US Constitution being the big one) because federal law is meant to trump state laws when they contradict each other.Why would the feds rule on a matter for the state?
The long and short of it is that when you can't rely on your local lawman to respect your basic rights, you take the case upstairs to the guy who'll ruin his life if he doesn't.