Here is a list of facts as we publically know:
1. The guns used were stolen not legally bought by the shooter. The fact that guns used in the shooting were bought legally by the shooter's mother has nothing to do with the shooter's possession of the weapons.

That is about the end of my list of publicly known confirmed facts.

The list of what we do not know:
Who purchased the ammo and was it bought legally?
What was the capacity of clips, magazines whatever used?
Who purchased those?
Was that a legal purchase?
What do we know about the shooters mental state or capacity? So far we have no confirmed information.
What did the mother do or not do or try to do in regards to his possible mental health issues?
Did laws hinder the mother's attempts to help her son?
Did laws hinder the mother's attempts to protect society in general from her son?

Just some food for thought.