At the time of his appointment, Mulloy was serving as diocesan administrator in the Rapid City, South Dakota, diocese, which said it received the allegation last month. It is highly unusual for a priest to be selected to be made bishop by the pope, then resign before that can happen. But the development serves to underline the pontiff's oft-stated resolve to crack down on predator priests as well as insist that any allegation of sex abuse be promptly investigated.