The Va. Tech shooter was known to play one of the most violent video games incessantly...his own video and image 'legacy' included poses and language similar to martial arts movies.

I am aware of how hard it is to show cause & effect, but many researcher are finding that long exposure to images of violence desensitizes one to real violence and is VERY often associated with anti-social behavior.

...and Sorcha's list, added to exposure to violence as a reaction to problems, sure is food for thought.