I agree that cops should be held to a higher standard than regular citizens when it comes to killing people. They are trained, they carry weapons as part of their job, and they should exercise extreme caution and discretion when using them against the people they are sworn to serve and protect. They should be required to learn how to de-escalate situations and use force only when there is an imminent and actual threat to their lives. They should also be charged with a crime when they kill someone, rather than getting off scot free after taking someone's life. If they had just cause, that will come out in court and they will be acquitted.
Cops are not above the law.
Cops work for the people, and cannot be allowed to kill with impunity.
I don't believe in the death penalty, and it doesn't apply in my country, but even if it did, cops are not judge, jury, and executioner. They don't have the right to decide if someone lives or dies, especially for crimes that would never have warranted the death penalty. They can't just claim self defense when they were not being attacked, when no weapon was used, or when the victim was running away from them.
None of that even has to include mention of race, but since black men disproportionately bear the brunt of police brutality, it also becomes a question of racism and measures should be taken to ensure that the law and it's application are unbiased.