There was recently a case of some cops who shot a pregnant teenager [0]. A few months before the prosecutor cleared the cops, the police union donated $10,000 to her campaign. I don't know if this was pay-to-play or not, but it creates very bad optics that undermines the appearance of justice. These kinds of events should always require an independent, maybe even unelected federal prosecutor, lead the investigation.

0: https://www.eastbayexpress.com/SevenDays/archives/2018/03/16...