Simple, just read through the DOJ reports, and I mean really read through them, it's a lot of information, but you'll see in their investigation a pattern of harassment directed at African Americans:
I kind of scratch my head when people say they don't buy the fact there is disproportionate treatment. There is the crime argument, but studies have looked at that issue and it is simply not true. Moreover, there is an issue of bad police officers staying on the force. In one study they found
most police officers (84%) have witnessed colleagues use excessive force on civilians, and most admit (61%) they don't report even serious criminal violations. The thing is, most police officers see it, it is done by a minority of police officers, but most do nothing about it. So guess what? It tarnishes all officers because the fact that these "bad apples" remain makes it appear that the behavior is condoned. People use the bad apple idiom and forget to finish it, "One bad apple spoils the bunch." That's a clear systemic problem. But there are also studies besides DOJ reports that concur with the findings of racial bias in policing (
What the Data Really Says About Police and Racial Bias). Nonetheless, we hear the same excuses, black people are more violent, it's about their level of crime, <insert dog whistle argument about black people or "black culture">, etc.