This is just so wrong, crule, sad and painfull as for all the other tragic killings of defenseless people over the years. Obviuosly if you would deny people in general owning weapon lawfully the number of available weapons would deminish, but the problem is still not the accessibility of weapons, the problem is fundamentaly the violent nature of our race and the twisted minds of disturbed people. Also the guy we want to not be able to get near a gun would be the only one having one - as of the criminal nature.
If there where no guns available innocent people would still be killed by mad men with a rock, car or a wooden stick or even by hand. One measure to prevent these things to happen would be to through healthcare systems identify the sick persons that are able to kill innocent for no "reason" (obviusly one could become sick instantly through poisoning or from other behavior altering causes) another measure would be to mix uniformed secuirty personell with none uniformed in certain areas along with high tech secriuty systems. A fundamental key is behavior profiling and police intelligence to be pro active - and for police intelligence to work effectivly the citizens need to report things that are odd, and for people to report things to be odd they need to identify odd things and take notice of them and care for peolpe around them - key word - Love.
To be frank, there have been people more or less close to the last couple of insane shooters - Utøya i Norway 2011, Batman shooting 2012 and this last massacre - relatives and friends who have felt something is wrong about these persons but failed to raise the alarm.
On the other hand we never get to hear about all the tragic incidents that where prevented from caring friends, relatives and just the person passing by with a caring mind.