Well, you're basically wrong on all counts.
First off: this would not be a difficult crime to pull off. There is no need for elaborate planning and careful plotting of escape routes. The only thing required is an eye for likely locations (far enough from traffic to to preclude witnesses, and close enough to merge quickly, and an open shot at a likely spot), a willingness and ability to kill, and the ability to blend into heavy traffic once the deed is done. There's no pattern, because there's no plan beyond finding spots to make a kill.
Second: Klebold and Harris demonstrated the ability of teens to pull of crimes like this. They chose to commit suicide; they could have as easily gone the sniper route. FWIW, I don't really think it's teens -- I think it's a couple of loser guys in their early 20s. And I think they read and loved Clancy's "Without Remorse," wherein an unhinged John Clark undertakes his own sniper spree.
Third: nobody here has blamed it on MTV, heavy metal, or video games. I, personally, blame it on the aforementioned nutjobs. However, MTV and metal would give encouragement to somebody already of a mind to do these things, and video games would provide a means of training (just as the 9/11 boys used video games to hone their piloting skills).