Good article by Professor Collins a Professor in Sociology at the University of Pennsylvania, written earlier this year

CLUES TO MASS RAMPAGE KILLERS: DEEP BACKSTAGE, HIDDEN ARSENAL, CLANDESTINE EXCITEMENT
SATURDAY, SEPTEMBER 1, 2012
Quote:
"If we are looking for ways to actually prevent violence, in the sequence of events and emotions that make up people's lives, we need to be aware of the different pathways leading to different kinds of violence. Since the pathways are different, we need to find solutions to each type at a time. The things that will diminish gang and street turf violence are not the things that will work on heading off school and other institutional rampage massacres. For these latter, I suggest there is a very strong clue that a massacre is being prepared: an isolated individual (or possibly a duo) engaged in an obsessive clandestine ritual around a hidden arsenal of weapons. To point this out is not to solve all the practical problems of taking action on it. But it is a step. "

Full article here