Ever since Columbine, I have wondered this very same thing. Even, before that, I think that the study of the causes of behavior of an active shooter or any one in society who has the capability of detaching emotionally like that is of great importance. In addition to understanding the psychology is the importance of knowing what gets through to a person to stop that behavior. There are stories of brave individuals as hostages who were able to appeal to some aspect in that individual to prevent chaos. That's why I like watching "Criminal Minds" (when I can bear to get past some of the gruesomeness). I watch to see the psychological profile that the characters, "Hotch" and Reed, etc. give to the police to predict the next action.
Years ago, I interpreted for deaf students in college Sociology classes and found that fascinating. Criminal Justice classes touch on behavioral profiiles a bit, but it's the Sociology classes, I feel, that have the studies that analyze behavior in the way you mention.
I often wonder where the studies are of psychologists who have gone into prisons, not to find out information for the police, but to really analyze any thread that runs through certain crimes. Of recent sadness for society are the teenage girls who terrorized another girl and said they wished she'd kill herself. Afterwards, one wrote on face book the equivalent of "I don't give a...." Baffling.