Death penalty without trial is usually reserved for foreigners, like Osama Bin Laden, and wedding parties in Afghanistan and journalists in Iraq. It's occasionally used on Americans, like the people in the Move On project in Philadelphia, or the Branch Davidians in Waco, Texas, but much less often. In either case it has to be authorized by someone high up in the federal government, cabinet level or above. An individual cop can't do it.

But cops can shoot if it's the only way to protect themselves or prevent other people from being killed. Everyone knows this, so when it happens it's either a case of suicide by police, which we have a lot of, or just plain old Darwinian elimination of the mentally less fit.

I personally have known two people who fought with cops, both of them white, and both of them violent-natured idiots. One was no real threat so he just got his butt kicked. The other was a professional boxer, who was able to inflict some damage. His face afterward was hard to look at.