Could We Have Stopped Cho?

It’s quite obvious that Cho Seung-Hui was a very disturbed individual with plenty of warning signs that he was quite capable of inflicting violence. The question is how does a free society act in a proactive manner to prevent unfathomable violence from such an individual?
I don’t have the answer. I am sure there are thousands of individuals who are as troubled as Cho but will never act on their impulses (except perhaps on themselves). I am not sure our society is able to determine which will ones will act out violently and which ones won’t. Our default position is that individuals will abide by the social contract that you don’t commit murder.
Since we are incapable of imagining that someone could commit such horrifying acts of senseless violence, it is difficult to stop someone beforehand. Would society be better off if we always acted as though people were going to follow through on the “worse case scenario?� If we did we may feel safer in the short term but what else would we lose?
Food for thought as our prayers and thoughts go out to Blacksburg, Virginia.