According to this reporter Paterno has to bear some of the responsibility. I don't know what the law is in PA or what's required to be reported by whom, but if Paterno knew what he is alleged to have known and if he pursued it no further than he did, than shame on him.
From the Fox sports report by Greg Couch -
“As the graduate assistant put the sneakers in his locker, he looked into the shower. He saw a naked boy, Victim 2, whose age he estimated to be ten years old, with his hands up against the wall, being subjected to anal intercourse by a naked Sandusky.’’
The assistant fled in fear and confusion. Much the same way a janitor fled after allegedly witnessing Sandusky engaged in a sexual act in the showers with a “young boy” — Victim 8, later described in the report as being “between the ages of 11 and 13.”
Shame on the grad assistant for not beating the crap out of Sandusky on the spot and then screaming to the police, the media and anyone else that would listen. While Paterno alleges that the graduate assistant didn't tell him specifically what was going on, shame on him for not pursuing it beyond passing the buck Paterno needs to go - now.