The "sex abuse" referred to in this indictment is not the usual physical sex abuse (touching, forced intercourse, etc). It refers to the acquisition of sexual images. Last December (2010), diocese officials discovered child porn images on his laptop and he is facing three state child pornography charges and 13 federal charges for possessing, producing and attempting to produce child porn.
It was not until May of this year that Bishop Finn notified law enforcement. During this period (December-May), Ratigan attended children’s birthday parties, spent weekends in the homes of parish families, hosted the Easter egg hunt and presided, with the bishop’s permission, at a girl’s First Communion. Some further indecent photos were taken during the Easter egg hunt.
Thus the indictment says that in this May-December window, abuse might have occurred due to the Bishop's delay in reporting the discovery of the pornography.
A little addition to your facts from the New York Times.
“The case has generated fury at a bishop who was already a polarizing figure in his diocese, and there are widespread calls for him to resign. Parishioners started a Facebook page called ’”Bishop Finn Must Go” and circulated a petition. An editorial in The Kansas City Star in June calling for the bishop to step down concluded that prosecutors must “’actively pursue all relevant criminal charges” against everyone involved.
Stoking much of the anger is the fact that only three years ago, Bishop Finn settled lawsuits with 47 plaintiffs in sexual abuse cases for $10 million and agreed to a long list of preventive measures, among them to report anyone suspected of being a pedophile immediately to law enforcement authorities.
Bishop Finn, who was appointed in 2005, alienated many of his priests and parishioners, and won praise from others, when he remade the diocese to conform with his traditionalist theological views. He is one of few bishops affiliated with the conservative movement Opus Dei.”
It seems that the Church in Kansas City is engaged in sort of fratricide between the conservative and liberal catholics.