Getting into the conversation late...
My comment is shaped from instances such as the Chinatown storekeeper who was arrested for assault and kidnapping for capturing the person who came back to shoplift from his store.
The problem here wasn't that he used force to arrest the shoplifter, but that he hogtied him and then kept him for hours. The criminal code allows anyone to arrest (within certain guidelines), using as much force as is reasonably necessary, but the offender must be delivered "FORTHWITH" (immediately!) to police. The shop owner had lots of time to make the delivery, or to call police to come after apprehending the shoplifter, but he did not.
If someone breaks into your house, how will you shoot them without a gun?
WHy are you shooting so soon? The law allows you to use deadly force only when you or others are in imminent risk of grievous harm/death. A guy who picks your lock and snoops in does not immediately pose such a threat. If you can see that the intruder is holding a gun, then you have reasonable grounds to use such force, but even then, you must be able to articulate that the person intended to use it to kill, not just intimidation.
or we could throw those billions into prisons
AKA Criminal re-training. A cop I know insists that it is only the stupid criminals that get caught. Then they go to prison and figure out how to be smart(er) criminals. You are better to find a way to keep certain kinds of offenders out of prison.
I feel sorry that he was shot so many times and even in the head, but with all the shooting in their schools, you have to put yourself in the cop's shoes.
When shot, the body succumbs to gravity very quickly, not at all a movie death. Firing at centre mass (chest area), and the head will find itself at that level pretty quickly. I feel bad for the kid's parents, but also that cop, who now has to live with killing, as you accurately put it, a misguided kid.
I have doubts on being a navy seal, one would expect that some one that trained in fire arms would remember the first rule is that you always treat the gun is if it is loaded even if you're sure it's not.
Don't forget they are also trained that they are "the best" and completely infallible, near invincible. Couple that with the fact he is only 22 (when guys tend to think they are invincible anyway), and you have a cocktail for carelessness.