When my father was a child, he saw two police officers shoot a black man to death in the back on a public street, in broad daylight, with no concern about who saw them. (1938).
I'm white, and I've been pulled over my white and black cops and never had to feel afraid. Now, I mind my manners & don't act stupid, but am I safe only because I behave myself, or also because I'm white?
I can't answer that question. In the early 1950s a white reporter disguised himself as black - he dyed his skin and shaved his head - and experienced a change in perspective. ("Black Like Me" - Griffith).
I'm sure black cops have roughed up blacks, and white cops have roughed up whites, and we don't hear much about it, so I'm not saying you're entirely wrong. I'm just saying there's a historical reason for why white cop on black suspect violence gets so much coverage, and it's not all ancient history.