What's so unusual about the feds investigating Pennsylvania dioceses?

The Associated Press reported Thursday that the U.S. Justice Department has opened an investigation of child sexual abuse in Pennsylvania’s Catholic dioceses, using subpoenas to demand confidential files and testimony from church leaders. The report cited two anonymous sources and noted that most of the state’s eight dioceses — including Allentown and Scranton — had confirmed receiving the subpoenas. Why are the feds interested in a state case?

https://www.mcall.com/news/breaking/mc-nws-feds-probe-diocese-clarified-20181018-story.html