The special commission of inquiry began on Monday with an opening address by counsel assisting, Julia Lonergan SC.
Over the next fortnight Commissioner Margaret Cunneen will investigate the circumstances in which Detective Chief Inspector Peter Fox, whose allegations of a church cover-up sparked the inquiry, was asked to stop probing certain matters.
She will hear evidence from senior police including two assistant commissioners and two superintendents, as well as former policeman and now state Nationals MP Troy Grant.
The inquiry will concentrate on two priests, serial sex offender Father Denis McAlinden and convicted paedophile Father James Fletcher, both now dead.
In July, Commissioner Cunneen will examine the extent to which Catholic church officials co-operated with police, including whether any investigation was hindered by the failure to report criminal offences.
Three senior Catholic officials will testify - current Archbishop of Adelaide Philip Wilson, who held senior positions in the Maitland-Newcastle diocese in the 1980s and early 90s, retired bishop of the diocese Michael Malone, and Australian Catholic Bishops Conference secretary Father Brian Lucas.
Its amended terms of reference include provisions to share information with the Royal Commission into child sexual abuse, ordered by Prime Minister Julia Gillard.
Commissioner Cunneen is due to report to the NSW government by September 30.
At the formal opening three months ago, she said the sexual abuse of children was "even more abhorrent" when committed by those in authority.