This is a very simple argument.
In the United States, people are innocent until proven guilty. The only way to prove guilt in our legal system is in a court of law.
Self-defense is a right as well.
As long as a person under arrest does not try to attack a police officer, under which the police officer may legally defend themselves under self-defense statutes, any non-violent person shot by a police officer is legally innocent.
Which means that almost every police shooting is a homicide.