Ratzinger's 1982 letter to Bishops, signed under his name, on taking over at the Congregation for the Doctrine of the Faith (aka Office of the Holy Inquisition) in 1981.
The letter reiterated that Crimens Solicittationis issued in 1962 under John XIII's signature was Canon Law. Within Crimen is the reasoning behind 'silencing' members of the church on the issue in full knowledge of the emerging abuse scandals in North America and elsewhere.
It also contains the instructions whereby an ecclesiastical court can hear the confession of a child abuser/clerical rapist. It contains no instruction to report anything to secular authorities.
Here is a later letter issue when he was Head of the CDF, reserving cases to his office and his office only on pain of excommunication. This was signed by him on 18th May 2001.
Bishop Accountability
He knew there was a serious problem with abuse issues at least as far back as 1982 and it is highly unlikely that he had never heard of the problem before then.
He's spent twenty years trying to keep the issue out of public hands.