The head of a religious group running services for Aboriginal people in the Northern Territory for 20 years knew nothing of horrendous abuse at one of its homes until a national inquiry was underway.

The conduct of Reverend Trevor Leggott, general director of Australian Indigenous Ministries (AIM) was roundly criticised on Monday by two barristers representing people who were horribly abused at the Retta Dixon home for Aboriginal children in the 1960s and 70s.

The sex abuse royal commission in September uncovered horrendous sexual, psychological and physical abuse of Aboriginal children - some of them very young - at the home.

But Rev Leggott admitted he was not really aware of the abuse until he read witness statements before the commission.

George Georgiou SC, representing three victims, told the commission Rev Leggott's recent apology was too little too late and his admission he only learnt of the abuse when the royal commission started asking questions was "extraordinary", as was his failure to acquaint himself with AIM's child protection procedures before giving evidence.

The commission has heard that it was not until 2013 that AIM had a manual on policies and procedures around child safety.

John Lawrence SC, for six of the victims, classed Rev Leggott's apology during his evidence to the commission as abject, insincere, cloying and made at "five-minutes-to-midnight".

The commission has been told of attempts to try an alleged perpetrator, Donald Henderson, one in 1976 and another in 2002.

Henderson worked as a house parent at Retta Dixon for 11 years and was convicted in 1985 of unrelated child sex abuse offences. He was fined $300 and placed on a good behaviour bond.

Counsel for the commission has already recommended a finding that apart from the public apology delivered by Rev Leggott no effort has been made to provide redress for victims.

The unconditional apology was repeated on Monday by AIM's lawyer Mark Thomas.

Mr Thomas argued that it was not AIM's failure Henderson was never tried. He blamed the Northern Territory legal process and said AIM was being made a "whipping boy" for its failure.

Mr Lawrence said the apology, now repeated three times, should have come a lot earlier and his clients would not accept it.

The response of AIM then and now "is not just inadequate, it is a disgrace", he said.

Rev Leggott has told the commission that AIM cannot afford to pay compensation. It has two properties that could be sold and this would mean stopping work done by the organisation.

Mr Lawrence said AIM needed to explain in more detail how asset protection was more important than compensating people who were horrendously abused in AIM's care.

Mr Thomas said AIM would participate in a national redress scheme.