It's a good question
But I was thinking about prevention rather than anticipation. Perhaps my premise is flawed, but it seems to me that it is something that we (societally, culturally, familially...) are doing wrong that provokes eventual violent behavior in some. Else we must revert to the idea that some people are just born bad.
Beyond that, to pick one particularly horrifying example, the mass murderer at Virginia Tech certainly raised some serious concerns in those who advised him, so perhaps anticipation was not entirely out of the question in that particular case.
I'd like to have a better world, but who wouldn't? The reality is that, no matter how many murderers are executed, we never seem to run out of them. Maybe it's time to try something different.
S