The inquiry is taking place at Banbridge Courthouse
The RUC and state agencies knew about sexual abuse at a boys’ home in County Down, in 1964, an abuse inquiry has heard.
They were alerted after a 14-year-old boy was abused by a De La Salle brother at Rubane House.
The details were revealed at the Historical Institutional Abuse (HIA) Inquiry.
A total of 13 Northern Ireland institutions are being investigated.
On Thursday, the inquiry heard that the order removed the perpetrator from the home and he was eventually expelled from the order.
An investigation by the De La Salle Irish headquarters deemed the incident “extremely grave” and concluded that the brother “would never again be allowed to have any contact with boys in any school”.
In a letter to Rome, seeking the brother’s dispensation from the order, he was described as having engaged in “grave immoral actions with a number of young boys”.
The 1964 letter also described him as “a positive danger to young boys”.
The inquiry also heard that details of the abuse were known at police headquarters in Belfast, but the brother was not prosecuted as he had moved to the Republic of Ireland.
A Ministry of Home Affairs letter from the time, read to the inquiry, concluded that “all concerned believed these were isolated incidents”.
Another departmental letter, linked to the incident, was marked “secret” and in the Northern Ireland Public Records Office, it was labelled “closed to public”.
In an opening submission on behalf of the De La Salle order, the brothers again publicly accepted and said they deeply regretted that boys in their care were abused.
The statement said: “They wish to offer their sincere and unreserved apology to all of those whom they failed to protect.
“The brothers recognise the sense of betrayal that the victims have experienced and the violation of trust caused by certain brothers within the order.
“They recognise that there have been failures to protect the victims.”
The HIA inquiry was set up in 2013 to investigate child abuse in residential institutions in Northern Ireland over a 73-year period, up to 1995.
About 200 former residents of Rubane House have made allegations of abuse.
A total of 55 former residents have come forward to the inquiry to allege that they were physically or sexually abused.