I would think it's more correlated with anything targeted to youth - video games and music more than movies.
You bet it is. We had riots at our HS in the 70's, I don't think there was a single shooting just a few people got knifed from what I remember. It's the media that has changed, the times were actually worse in those days but people didn't have the notion that you use a gun to solve all of your problems. So where are they getting the idea ?