This is exactly why California in the United States is so strict on issuing guns to Security Officers. (Security Officer=Armed Security Guard, Loss Prevention, Body Guard, and a variety of other variations of the same field, by basic training definition).
I'm very sorry for the loss of your classmates and their family members, Orel. It is always very unfortunate when things like this happen. My best guess is he probably just "snapped" after he found out his girlfriend was cheating, and couldn't handle it, so he went on the rampage. It's sadly all too common these days.
For the lives lost, I hope they rest in peace, and those they left behind can find a way to eventually cope with their losses. Losing a loved one never gets any easier. It is one of the horrible parts of life itself.