The best we can really do is tighten all of the bolts that we can see, and hope the leak slows down to an acceptable level. Improve gun ownership laws, improve our handling of the mentally ill, assist those experiencing crippling poverty, etc. Attack all the angles reasonably to get crime down to a reasonable level.
(And an acceptable level cannot be "no incidents". To accomplish that would require a police state. We must accept that once in a while horrific things will happen, and there was nothing that could reasonably be done to prevent it. i.e., shit happens.)