I guess the shooter was not aware that guns were prohibited on campus. But do not worry, apparently he was not a student and we all know students are worse. Legally armed students are bad; nutjobs coming into campus and shooting old ladies are not so bad.
UPDATE: Apparently it is also a domestic situation gone bad. Thomas Franklin May III had a restraining order issued against him for domestic violence and it seems that the magical powers of legal papers did not do a damn thing to stop him from shooting the victims.
So, two for the price of one: Gun Free Zones and Restraining Orders: Deadly Sense of Security.