Mike,
One thing that should be reviewed is the success of gun registration has had where it has been utilized in those states and cities that have gun registration laws. Are they being successful in these locals? If so how? If not then why not?
Personally I am not for adding a new law on this matter, because it isn't going to accomplish anything anyway. Mass murderers will still pop up from time to time and these murderers will figure out how to kill. Perhaps taking guns away from people, will make the mass murders even worse, as they my start using weapons of mass destruction instead of point destruction.
With what I personally own, if I decided to go on a rampage and kill as many people as I could, the last thing I would use is a gun anyway. Arson, which is the easiest way, or a heavy vehicle in an area with a dense concentration of people, would be the best methods to take out as many folks as possible.
The only type of law change in my opinion that would work would be to address the issue of mental illness head on. Examine those countries that do not have cases of mass murderers and see what they are doing differently than our mental health care system, and try to emulate. If they are doing nothing significantly different, then spend some money to research what triggers there are in society that is creating these types of people.
Removing or banning guns from society...well that ship sailed a long time ago. It isn't going to happen. One thing that has to be understood, is that personal freedom does have negative consequences. It always has. To eliminate and or minimize those negative consequences requires a restriction of personal freedom. People will have to determine if eliminating mass murderers is worth having restrictions on personal freedom. With all things considered, though someone in this country has a greater risk of getting killed in a terrorist attack than to being killed in a mass murder; and as you and others have pointed out in other posts, the likelihood of such things are pretty much nil.
I pray for the families of those who lost their lives, and for those, and their families who have been tragically affected by these attacks.