There may not be formal government programs that presriptively sanction the murder and decimation of minority communities by the American constabulary but the law also historically has given merit to "disparate impact".
Furthermore Van Dyke's conviction came with mitigating factors that I will passionately argue create the conditions for disparate impact when black Americans are killed by state actors in the form of local police officers.
This IMO supersedes any argument that we lack government policy that sanctions police brutality and points to a direct need for police reform which is the root of a statement like "Black lives matter".
We do have a few wackos here and there which is unavoidable.