[quote=mdk]
All of them. 
[/quote]

What you're trying to say is, "Psychos happen." I tend to agree. I also agree with the Jungian 'thing' about the dark side of human nature. ;)

It'd be nice to prevent these once and for all, but people are not merely good at killing and have violent impulses, but they are also very adaptable and creative. On another note, the family warned the police, and this kid had mental issues and handguns. I'm sure more will come out on how he acquired them, and that's something to pay attention to. I won't jump the gun by speculating on whether or not they were a legal acquisition. 

The ball was dropped, but I also tend to think that in a lot of cases where the ball is dropped, there's a cry for heads to roll before the guys in charge can fix the mistakes of their underlings. Sometimes the buck stops there a little too fast, and otherwise capable people aren't given the time they need to fix a problem.