Well I see it like this:
In order for the book induced murder to occur, what's required? The murderer him/herself, and the book. If either is missing, there would have been no death. I don't deny the fact that murder should take majority of responsibilities, but I still think the book is at least partially responsible.
That's equivalent to saying for a stabbing to occur you need the person doing the stabbing, and a knife.
Should we start a war on cutlery? Probably not.