A senior NSW police officer who blew the whistle on an alleged cover-up of clergy child abuse says independent investigators will be crucial to the royal commission on abuse.
Prime Minister Julia Gillard on Friday will announce the appointment of six royal commissioners to investigate cases of child sexual abuse and the terms of reference for their inquiry.
The commissioners, to be appointed for three years, will be asked to provide an interim report within 18 months.
The commission will have an investigative unit to examine specific cases of sexual assault and institutional secrecy.
Detective Chief Inspector Peter Fox said he was pleased to hear the investigative unit would be established.
He said police investigations into abuse had been ad hoc across the states and an independent body of seconded police officers would be valuable.
"The police are those who are best suited to make and conduct investigations, but they have got to be answerable to the royal commission, not state or territory bodies," he told ABC television on Friday.
He said many police task forces had been set up in the past, but there had been no coordinated approach.
Insp Fox said the inquiry also needed to examine how church law interacted with criminal law.
Most church law worked well, but some parts were dysfunctional, he said.
"Effectively they overrule any state or national laws on how their employees, that is the clergy, are to treat reported crimes and that to me is very alarming."