goodlifes usual banal attempted defence of god aside, for those who do believe in a benevolent god, examples of senseless killing like the one that has just occurred must be difficult to reconcile with their faith in this avuncular entity.
Most answers from the faithful will offer platitudes - "its not gods fault, it is imperfect humans", or "god gave us free will, its up to us what to do with it." Others will offer some sort of karmic balance answer - "sometimes bad things happen to good people, but it will all balance out in the end." All these answers are unsatisfactory, and to me represent a more fundamental point, which is that god is a man made construct, born out of fear and imagination, lingering on through hidebound tradition and irrational faith.
For me, vascops answer pretty much sums it up exactly. No god, just a combination of tragic circumstances and an extremely unstable young man trying to achieve who knows what with a barrage of bullets from a high powered, rapid firing high capacity weapon, resulting in the slaughter of the innocents.
Epicurus was probably right.
"Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?"