The NSW Police Integrity Commission (PIC) has opened an investigation into agreements between the state's police force and the Catholic Church which may have enabled the church to conceal information about child sexual abuse.

Last year, the ABC's Lateline reported accusations that the church tried to strike a formal arrangement with police over how to handle abuse allegations and what information would be handed over for investigation.

There are questions over whether the memorandum of understanding was ever signed, approved or even in operation.

Operation Protea has now been set up to investigate such arrangements and whether there was any police misconduct between 1998 and 2005.

It will also look at the secondment of a senior police officer to an internal church committee which dealt with allegations of child abuse by clergy.

NSW Greens MP David Shoebridge, who accessed the police documents under Freedom of Information laws more than a year ago, said it was a welcome development.

"It is clearly a matter of deep and serious concern to the integrity commission," he said.

"The fact they are holding a public hearing is further confirmation that this is a serious inquiry, but it needs to go to the highest levels of NSW Police."

Mr Shoebridge said the documents he obtained raised serious questions.

"It became apparent that there was a formal MOU between the police and the church," he said.

"We saw this police officer engaged on the internal committee, and when we asked for the details of the evidence that had been given to that police officer, we were told that there was a protocol in place that either all of the evidence was returned by the police officer or anything that was retained by the police was shredded.

"Now how on Earth that came to be is an absolutely extraordinary set of circumstances, a deep potential conflict of interest for the police, and why, I assume, the PIC is taking such a careful view of it."

While it might be argued that such cooperation enabled an exchange of intelligence, Mr Shoebridge said it was difficult to justify such an arrangement.

"There is a fundamental problem when you effectively co-opt the police into your own internal inquiries, and of course the church has an obligation under the criminal law here in NSW to report to police instances of child abuse that would amount to an indictable crime.

"Almost certainly every one of the alleged allegations would have satisfied that obligation to have to report, and you can only speculate that the church may well have set up this institution and this arrangement with the police seeking to satisfy their reporting obligations under the Crimes Act and therefore avoid prosecution for failing to report to the police."

The Catholic Church's Truth Justice and Healing Council said it welcomed the PIC's inquiry.

The council said it would cooperate fully with any investigation that could provide greater clarity around the relationship between police and the church in relation to child sexual abuse.

The public hearing will be held on October 13 in Sydney.