Many of them are experienced and trained. The man who shot Renee Good served in Iraq, worked for Border Patrol for two decades and was literally a firearms instructor[1].
This is just what cops, reactionaries and psychopaths will do when they know that they have carte blanche to do anything they want, including murder.
No amount of "training" will fix this. It isn't an accident, it isn't incompetence, it is deliberate and wanton.
[1] https://en.wikipedia.org/wiki/Killing_of_Ren%C3%A9e_Good#Jon...