Y'know, it seems we have shootings all the time here in the US. It has become almost normal, and we've become almost numb to it.
Punishment is meant not only to punish, but to teach as well. In the case of the penal system, rehabilitation is a word not commonly used anymore.
I do not believe that the threat of punishment is a deterrent to people who would otherwise be inclined to commit a crime of such a magnitude. If that was the case, we wouldn't have vicious crimes at all. There are, I think, some people who are just plain evil. I have no idea what to do with them. But the rest can find assistance with rehabilitation and job placement.
There are so many other variables that one post and a reply can't cover nearly all of them, of course; for instance, why would a drug dealer care about working at minimum wage when he can get all the much more for selling drugs? You're spot on about needing to identify the source of the problem. Personally, I think inequality of opportunity has something to do with it. I don't know how to fix that, either.