NSW police officers discussed whether a "Catholic mafia" existed within the force, deliberately hindering the investigation of pedophile priests, an inquiry has heard.

Giving evidence at the NSW Special Commission of Inquiry into child sex abuse, Detective Chief Inspector Peter Fox said he discussed these fears in 2002 with the current state Nationals MP, Troy Grant, then a serving officer.

Mr Grant "was highly critical of some senior police at Newcastle in what he perceived to be hindering his investigation" into alleged child abuse by clergy, Detective Fox said.

The MP, who will give evidence tomorrow, used the phrase "Catholic mafia" to describe two particular officers he felt were deliberately asking him to work on other criminal investigations, Detective Fox said.

"He was referring to what he perceived to be police who he felt to be aligned to the Catholic Church, who were attempting to discourage investigations into clergy," he said.

During 2005-6, Detective Fox also claimed to have written two internal reports calling for a police task force to be established to investigate a possible pedophile ring operating within the Catholic Church in Newcastle and the Hunter Valley.

He had subsequently been unable to find any record of these reports, the police officer said.

Earlier at the hearing, Detective Fox said he did not tell his superiors within the police about investigations he was pursuing into the church.

Detective Fox's office was subsequently searched by police officers looking for material on child abuse within the church. This material included a written complaint about pedophile priest Jim Fletcher.

The special commission is investigating claims by Detective Fox that he was told not to investigate an alleged cover-up by church officials of child abuse allegedly committed by priests within the diocese of Maitland-Newcastle, in NSW.

Counsel assisting the inquiry, Julia Lonergan, told this morning's hearing that senior police claimed Detective Fox was assigned to a different Local Area Command to that conducting the investigation, and as such, was not formally part of the inquiry.

The policeman had a history of pursuing his own investigations into alleged pedophile priests, Ms Lonegan, SC, said.

"He pursued certain investigations that he kept confidential to himself rather than logging them through police channels," she said.

Commissioner Margaret Cunneen, SC, said evidence provided by Detective Fox had also been passed to the Royal Commission into institutional responses to child abuse for further investigation.

"It can be very difficult for children to break their silence about sexual abuse and, when they do, the collective responsibility to take action weighs heavily on us all," Ms Cunneen said.

The hearing continues.