With the disclaimer that it's been a few years since I took torts and Con law (so take this with a grain of salt), sovereign immunity doesn't protect state actors from violations of civil rights. In fact, 42 USC 1983
specifically creates a federal cause of action for violation of federal constitutional and statutory rights. And it's not limited to just federal actors. It's "any person" who "under color of [authority]" deprives a person of their federal civil rights. If I remember correctly, the theory behind this statute is that the federal government can waive the states' sovereign immunity under the auspices of the 14th Amendment, since it came after the 11th Amendment, which solidified the states' sovereign immunity. So assuming everything is as it's stated in the summary, Rachner would have a federal cause of action against the police department.