It was classed as an act of "domestic terrorism", and it may very well be, but no similar acts will be avoided in the future by disarming honest citizens
Notwithstanding, the young shooter is definitely sending his heartfelt thanks to the management of the shopping mall for allowing him to walk in straight through the front door with his rifle in hand and ready to use with no security personnel around to stop him dead cold before he could start shooting.
He'll also be grateful to all the stupid anti-gun pundits who will help him to become famous by talking about him, guns and shootings left and right without the slightest knowledge of gun safety, laws and mental illness.
It's only thanks to the precious help of such incompetents if another madman could reach his goal.
On July 9, 2019, Walmart announced they would stop selling firearms in New Mexico after a new "public safety" laws was introduced in the State expanding background checks: the company would have been forced to conduct background checks for guns it would't sell, and the management was also worried that people bringing guns into Walmarts to register them would create safety issues for associates and customers.
What neither Walmart, nor goverments and politicians worldwide seem willing to understand that madmen and mass shooters would not ask any permission or follow any law once they decide to act it out. Much less do they care about stupid "no guns allowed" signs and other rules imposed by managers and lawyers to protect themselves from any liability in case of a... well, a shooting.
If Walmart – or any other similar establishment – would just stop follow anti-gunners (or self-appointed gun control advocates at large) and would instead carefully select, hire, properly equip and train private security personnel to a good level, criminals and madmen would think twice before barging in with a loaded gun.
And this, leaving the whole "Gun-Free Zone" argument aside just for the sake of brevity.
This is the price we pay for living in a world of incompetent quacks.