I think anyone would agree the deceased made poor choices and didn't contribute to society - but that's not that issue at hand; nor would anyone oppose harsher sentences for criminals, which again, not the underlying issue here.
He was ordered not to shoot, he willingly did, from the sounds of it, knowingly expecting casualties. If you can't aim 00 buckshot at 15 ft towards a man's lower torso - you shouldn't be holding the shotgun in the first place.
I would like to know how an undercover or uniformed Police officer would have handled the situation put in a similar spot.