There will be plenty of time to assess blame. But let's not be too hasty to assign it. Let the university administration have a few days to explain why they didn't order a general evacuation. Let the police explain why they waited outside while shots were audibly emanating from the building. And more than anything else, let's remember that this was a rampage by a lone nut.
We know he was apparently a student
There are those who will blame the guns. This is stupid, since if the guns were legally confiscated, those who wanted to do something evil would still be able to come by them (even if it was on the black market), and then things would go as they are now, or worse. To be honest, I favor CCW laws, with appropriate training and certification. One never hears about someone going berserk with a gun in an army barracks or a police station, for example. It's invariably where they expect to find defenseless (as in unarmed) people.
There are also those who will blame society (video games, music, etc.) Now I've got my problems with society, but if you hear someone say this then just keep in mind that this fellow was exposed to Korean, not American society earlier in life.
As I said, and with the recent example of the Duke rape case in mind, let's take a stop back, let the authorities do their job and see what we learn.