Unfortunately, I stopped being shocked by these mass shootings in America many years ago, many shooting incidents ago. Columbine, and all the factors around it brought to life in Michael Moore's Bowling For Columbine showed America has a gun homicide problem way out of whack compared to the rest of the Western World. That was twenty years ago though, and incident after incident just keeps happening. So I've thrown up my hands about it changing, unless it happens to the rich and powerful somewhere.
Yes, every country has incidents where someone snaps and goes on a mass killing spree. But Americans do it SO much more compared to the rest,,, if they don't see they have a problem, then don't live there and count yourself lucky.
The shooter legally bought those assault rifles, apparently. I'll say it again - no one outside of the police or military should have access to assault weapons. Neither are needed for home defense or hunting. Does the 'right to bear arms' mean you can own anything, like a nuclear weapon of your own?