The rising instances of police killing civilians, how many has to be killed before there is any accountability?

This has been a issue for decades most importantly with the African- American communities, why does the step by step procedures of subduing a suspect always goes to a murdered African- American? But in instances where there is actually a person not of color being violent and belligerent they are peacefully subdued. The statistics and facts do not lie, we make up 13% percent of the U.S Population yet 37% are dying (2015). Please can there be more done in terms of accountability, as we have mothers, aunts, husbands etc... losing their loved ones. and the only punishment received is desk duty and a civil lawsuit being paid by the cities they work for but civilians are being prosecuted to the fullest extent of the law. What type of message is that sending out?