Risk of being killed by police use of force in the United States by age, race–ethnicity, and sex - Peer Reveiwed 49 sources.
"Deadly Discretion: The Failure of
Police Use of Force Policies to Meet Fundamental International Human Rights Law and Standards - Study on 20 large metro forces.
What the data say about police brutality and racial bias — and which reforms might work - Article, not peer-reviewed only 18 sources. However, it's being published by Nature which is the most prestigious scientific journal on earth.
Here's a 20-year-old study that says improper force is applied in 38% of encounters (where force is applied).
Here's a study that suggests that police corruption spreads like a communicable disease
That should start you off.