Of course, if the priest has done something wrong specifically regarding Church business, he can be prosecuted in a Church trial, but this abuse was in the secular criminal realm, so the Bishop would not have any authority over it.
No, actually it is also a violation of the canons. The secular state may well prosecute the crime, and if the bishop learns of it from the victim, rather than the perpetrator in the context of a confession, he has a duty to turn the criminous clerk over to the state. He also has a duty to depose the priest, which is not something the state can do.