Under Title 18 Part 1 Chapter 1 Section 4 of the United States Code, Joe Paterno can he charged in Federal court for failing to reveal to "Civil or Military Authorities" the crime.

Whoever, having knowledge of the actual commission of a felony cognizable by a court of the United States, conceals and does not as soon as possible make known the same to some judge or other person in civil or military authority under the United States, shall be fined under this title or imprisoned not more than three years, or both.
I've Bolded the Key phrase of the law which applies and could lead to federal charges should they pursue them.