From what I read people who knew him said he was a quiet type and was really smart too. Unless the state declared him metally ill I don't see how you could have prevented this.
Everything I read stated that he had plenty of problems. Knowing that her kid had problems, she should not have had guns in the house. The blood is on her hands as well, not that it matters anymore. In her case, nothing can be done now, but in the future, if parents have guns in their house and their kid shows signs of mental illness and they do nothing about it, they should be held responsible as well. At the very least, the guns should have been more securely stored. Sorry, I will not buy that nothing could have been done. That's cop-out. If you know you're kid has problems and you choose to a) do nothing about it and b) keep guns within his reach, and he goes out and shoots up a school with those guns, you are responsible. But by all means, stick with the apathy. How very American. Don't worry, nothing will be done about it.