The fault lies within the home itself. There were no safety systems, no safe, no lock and key, no out of reach system to prevent this guy from obtaining his weapon. I doubt the black market would be affordable for him.
All of us could argue on how to curtail the threat of gun violence. It will always be here, but the real question is how to reduce...not prevent.
Reduction decreases frequency which will help law enforcement manage gun crimes much easier. It will also be more economical as gun owners and sellers will not be subjected to hefty/costly regulations due to others stupidity.
Educate our country on gun operations and what they are for. Defense, not offense. Teach people how to store a gun safely, how to manage it safely, and the proper ways to use and discharge the system using high velocity projectiles.
I have an opinion on ownership of military grade weapons though. They are for military, not civilian. You do not need a semi- or full- automatic gun with a magazine to defend yourself unless you are a warrior. A simple pistol or rifle would do. I don't care if you buy 'assault weapons' for a hobby, there should be a reason why you should NOT own them!
I am not a gun enthusiast, owner, nor user. However, I feel that legally we are granted special rights to bear arms, whether guns, knives, Molotov cocktails, Chuck Norris, etc... and that our government should respect that.
Oh, and BTW, Obama cannot legally take your guns away. See, there is this piece of paper, called the Constitution... you should check it out sometime!
If he does, his power as president is illegitimate. Same goes for congress and the supreme court.