I think Silence of the Lambs was a big factor, too. A plausible starting point for the twin trends of obsession with procedural stuff, especially psychological, and the serial killer as the lazy crime writers friend (complete with descriptions of horrible acts), which added together lead to a lot of explicitly portrayed nastiness.

I love Silence of the Lambs (and Red Dragon), but like Tolkien I can love the original while thinking they have been way too influential.