There are two novels that can change a bookish fourteen-year old's life: The Lord of the Rings and Atlas Shrugged. One is a childish fantasy that often engenders a lifelong obsession with its unbelievable heroes, leading to an emotionally stunted, socially crippled adulthood, unable to deal with the real world. The other, of course, involves orcs.... John Rogers
All of the above and then some.
A culture that glorifies gun violence will spawn gun violence.
"Most responsible" doesn't leave room for multiple options, so I specified the shooter -- nobody is more responsible for the actions of an adult than said adult.
That said, the way society looks at mental illness in general and the way we "care" for people with mental illness is disgusting and needs to change.
If we're going to address this kind of violence definitively we need to attack it from multiple angles at once -- and the main thrust needs to be the perception and treatment of mental illness.
That said, the media does play a huge role, but it goes full circle because the media is simply a business providing its consumers with what they want. Trying to blame the media for how people use what is reported is no different than blaming gun manufactures for how guns are used.