I never blamed the guns, the epidemic of mental illness is the problem, guns are just an easy tool to cause the most death and destruction when the ill person decides he (or she) has had enough. There are so many people who are mentally ill that we could never build enough institutions to hold them all, and who would pay for it?
An armed guard at schools would help but would probably only slow someone like this down, take the cop by surprise and he would just be the first fatality.
Where there is a will there is a way, and anything you do to stop things like this from happening can be overcome with enough forethought.
People need to speak up and report people to the authorities who they believe are ill and might do something like this, next time one of the dead might be someone you love.