As we see in the killing of unarmed citizens, too many police officers are acting as judge, jury, and executioner on American streets.
A new law should be passed to make it incumbent on police departments to prove, with as much evidence as would be required for self-defense in a real court of law, why they had the right and the absolute necessity to take the life of a citizen following every single case of deadly force.
Let the police provide the evidence to support their claim of having no other choice but to kill by producing evidence to this effect in a court of law.
If they cannot prove that their actions meet the legal definitions already decided by Congress and SCOTUS, let the police department and the individual officers be either civilly or criminally liable.