Psychiatrist and Cornell Medical School professor Richard Friedman acknowledges in the NYTimes this week that our abilities to predict who is likely to be violent are no better than chance. This is the partly the result of the fact that mass killings distort our understandings of violence and mental illness - the vast majority of the mentally ill are not violent and are more likely to be victims of crimes rather than perpetuators. Secondly, many of these violent people avoid contact with the mental health care system. It's also clear that while many killers are young, lonely, and angry young men - there are countless more young, lonely, angry men who aren't killers. That's far too large a group to criminalize.

What to do then if human behavior proves to be too complex and unpredictable to submit to our models or diagnostic protocols? Friedman writes: "We have always had - and always will have - Adam Lanzas and Elliot Rodgers." There will always be people whose horrific behavior we will never be able to understand or explain. Rather than trying to pick out who will do what, let's try to control the expression of violence. Inexplicable acts of violence may be inevitable - let's make it more difficult for them to be so deadly. That involves gun restrictions for those with histories of serious psychiatric illness, but also perhaps gun restrictions for all of us: isn't the mere ownership of an assault weapon enough of a clue that something might go wrong?