All the talk of citizen heros who could've killed the VT shooter is misleading at the very least. A discussion at Daily Kos. There are sociopaths everywhere: US, India, Iraq, Sudan. How dangerous a weapon they get and how easily they get those weapons makes a big difference in what headlines you see: "Loner attacks students with a knife. One seriously wounded" or "32 people killed when a shooter opened fire and systematically executed people in a classroom".
For the level of planning of this attack, the headline could just as easily been, "Loner pours gasoline into lecture hall; 150 incinerated."