At the very least, there need to be extremely strict, and strictly enforced gun ownership laws.
Honestly, even if we had the strictest [edit: ownership] laws possible, I think this guy would’ve slipped through the cracks. He had no criminal history, he showed no signs of planning anything like this, and he had no discernible motive (at least right now, these may change as more information is released). He was just an average 60 year old man with time to waste and a hobby.