I never said it wasn't irrelevant- I'm not sure why folks think this is what I am saying.
Maybe I just can't convey properly what I am trying to say. I don't know, sometimes things get misinterpreted online.
I understood what you meant.
It's very hard to disentangle the influence of inner psychological demons vs the involvement of external violent influences.
To cite an extreme example, in one case I followed, the killer (same age) had a copy of Silence of the Lambs on his coffee table. So was he inspired by the book and the figure of Hannibal L? Then how come the millions of others who read it, didn't also go out and kill people?
Edited to reword last paragraph.