The media likes sensational news.
"Innocent unarmed black man murdered by white police officer."
They just must make it about race. When whites are killed by police, heck, that's nothing new. People die all the time. But black? That's controversial. It will draw more eyeballs to their websites. I think the media negatively contributes to all this. If you label police the bad guys then eventaully people get inured to police brutality. They accept it as the norm.
There is a fact in life that there will always be a bad seed in everything. They are a number of good cops who would put their lives on line to save a citizen. In the midst of this group will be a bad cop who will abuse power. It becomes difficult to trust the police depending on the experience one has had from the force.