It only becomes a police issue when they become violent. The reality is that young, isolated males are genetically pre-disposed to commit this types of crimes. Combine their genetic pre-disposition with societal influence and you get ticking time bombs - guns or no guns.
Your call to make this about race but its not - it's about parenting, mental health, a shitty system...etc. I could go on and on. Gang violence is a different cup of tea. Brown on brown, black on black violoence is anchored by socio economic conditions. Walking into a classroom of young children and shooting them in cold blood and watching them bleed out (much faster for small bodies) is different - the warning signs are usually there and they are usually ignored. This will happen again, I have no doubt.
Next time lets hope the school doors are locked, cops with balls show up, and someone takes charge. Preferably there will be a system in place that provides enough of an obstacle that these types of assholes don't get inside of a school. I dont' think that is too much to ask for. As a test, go and try to gain access to a corporate building somewhere. Most high value corporations spend millions of $$ on phyisical security. Amazing what badge readers do to deter entry.