In a just world this cop would be put in prison for animal abuse not only for shooting it unjustly but leaving to writhe there in pain instead of finishing the job.

There was no charging whatsoever, the dog was protecting it's home from a clearly violent stranger. We have laws for loose dogs for a reason, animal control comes and hauls them away, cops don't show up for animal related issues like this and murder them in cold blood.

The dog never "Charged" him, whether or not it charged the mailman we will never know but since there is no mailman in sight I think it's safe to assume he doesn't exist or, at the very least, did the noble thing and left the dog alone and got on with his duties.