They need better screening. Anyone that would shoot a man in the back like that, and then try to plant a taser, is not someone who should ever put on a uniform.
Unfortunately, it's a snowball effect. As police come under more and more scrutiny, the job becomes more difficult and stressful. It comes to the point where no one in their right mind would want to be a police officer.
No argument with you that it is a difficult and often thankless job. In my area they are paid, benefited and very well pensioned.
Times have changed, like I or not. It used to be taken for granted that police would chase the homeless out of town. Now if asked, a police officer will say "it isn't against the law to be homeless."
But that same officer has been trained that if he unholsters his weapon, he unloads it high center mass.
The trick is screening them, and training them when to shoot, IMO. (or beat, kick, baton, etc. for how long)
There is a fresh video today, of an incident in San Bernardino CA, whereby many officers go after a guy who has been tased, lies on his stomach, puts his hands behind his back.
But after the officers cuff him, they go on beating and kicking him for several minutes, all under the watchfull eye of a news helicopter.
