I'm utterly saddened by the shooting in Arizona. And equally impressed by the folks who tackled the shooter, disarmed him, and held him until the police/sheriffs got there. It's somewhat sort of amazing to me that they didn't try to kill him in anger.
When I was a kid, my neighbors had a son who was a fair bit older who was seriously mentally ill. I never met him, but my neighbors were fearful that they would someday be told that their son had killed someone. This was shortly after the state decided it would no longer house/treat mentally ill people who hadn't actually been found guilty of a crime, and put them on the street. My neighbor's son was one of those; as an adult, he could do what he wanted, and his parents couldn't do anything really. But they lived with this fear.
I'm thinking that the shooter's family is living that nightmare now, as are the families of the victims in a different way.
(Let me acknowledge that people who are mentally ill are FAR more likely to be victims of crime, especially violent crime, than to commit such crimes themselves.)