I mentioned magazines. Capping magazine sizes and the amount of ammo a person can purchase at once would be a great start for making sure shit like this doesn't happen. The previous assault rifle ban would also ban long guns that could be modified to be fully auto.
But, sure, do nothing. Watch the copycats roll in.
I don't know I how I feel about that now but I hated it when they limited magazine size in the 90's. I was much more comfortable with knowing I had more rounds when I used to carry. What capacity would be a good number to you? I'm all for strict background checks but I don't know that an AR-15 is any worse than a hunting riffle assuming its not full auto of course.