This looks like a mater for the state.
If you check the link by tommyboy you'll see that Dillon was also arrested for rape in 1998 but no charges were ever brought against him.
In instances where someone commits a serious crime like rape or murder but the state makes no effort to prosecute or only a pro forma effort that fails to convict the Feds often step in and prosecutes the crime as a civil rights violation. It's something that I'm ambivalent about. Sometimes its good because otherwise justice would never be served, however, such prosecutions are all too often politically motivated.
the crime is deprivation of rights "under color of law"; the ordinary rapist doesn't have the force of the state behind him. A judge or prosecutor or sheriff who does it in apparent connection with official duty does. Or the sheriff who beats you to death (see a case from the 1940s in the Supreme Court, US v. Screws)(Yes, the sheriff's name really was Screws!)