I find this comment left by an anonymous person somewhere in the blogosphere to be an accurate, if oversimplified description of people like the Montreal college slayer
I believe there are many people like Gill in the world. Living on the edge of reality and fantasy, they internalize their pain. Being bullied is a part of modern adolesence. Either you are a bully or smart and tough enough to deal with it or become a professional victim.
Professional victims often take refuge in the fantasy revenge world offered by violent video games and the fantasy world begins to sabotage their view of reality.
I have known quite a few people who have literally walked over the edge and embraced fantasies.
Some have become wonderful eccentrics, living a fantasy beyond simple art.
Some have fallen into a pit and try to drag anything around them into it.
This phenomena of the wounded victim loner merging violent famtasies into horribly obscene reality seems to be a symptom of our modern world.