If that officer was fast enough to realize that "Action is faster than reaction" and shoot to kill in the back of the head, he was fast enough to back off.
Why should police officer have to back off in light of a perp resisting arrest?
The fact you feel the need to ask that question speaks volumes. Resisting arrest is not an automatic death sentence penalty in the USA.
Pet peeve: "This sub-task is no cause for a reaction to the whole"
No drop of water is responsible for the flood.
"Since when is death the penalty for a BLACK PERSON to simply twitch their finger slightly!!!!?one1?"
Ever since that person chose to hold a gun, point it at someone, and position that finger over the trigger, obviously.
"Since when is having a run in the park deserving of EXECUTION BY THE GOVERNMENT"
Ever since that person chose to wield a knife and run directly at a group of children while screaming, "I'll kill them all!!!", obviously.
and, most relevantly, "since when does having a little scuffle with someone create cause to be shot??"
Ever since that person chose to have a scuffle with a clearly identified police officer and attempt to take their weapon(s).