Elephant by Gus Van Sant is a great film about this subject, but recently I rented Zero Day and it blew me away, I give it 5/5. This film was a first film made on a small budget and it's a great example of intelligent film making for little money.
It's all done home-movie style and this makes it even more intimate. These kids are such 'nice' kids, and their motivations for their actions are absolutely fascinating; they have such a simple, nihilistic vision and yet on one level they actually believe that their actions will end up making the world a better place. And that's the thing that gets me, on some level people who take such violent actions actually believe that they're going to improve their world. There is no anger in their actions, its more like a school project that they've undertaken. The film comes across as a 'how to' guide, especially the scene where they outline how to make pipe bombs - extremely ordinary and chilling at the same time. And its amazing how easily they obtain guns - and this is the most important aspect of this film - in the US kids can get guns really easily and if they didn't have access to them they wouldn't be able to do it.
They are almost like suicide bombers, but not really because there is no religious motivation, the whole thing for them is like the biggest adventure of their lives. They embody something so suicidal & destructive en masse in our culture, particularly amongst young men - and they see this as a solution to the blandness of the culture that they are raised in.
This movie had a profound effect on me, I'm not sure I can actually articulate it fully. In the end there is no hope but the viewer is so affected because you have bonded with these guys and on some level you empathise with them, you understand how their lives have brought them to this solution. A serious trip.
I had to watch the 'making of' on this one to convince myself that it wasn't real. I've been watching some intense DVDs lately, tonight I'm watching Crash - based on the Ballard book of the same name. I couldn't get through the book as it was too gross (lots of long-winded highly-descriptive passages on bodily fluids etc.).
I think after this spate of the sick & perverse I might need a light romantic comedy ;-)