NSW investigation into Cunneen 'a debacle'

A "debacle" and an "absolute grotesquery".

The NSW corruption watchdog's controversial investigation into deputy crown prosecutor Margaret Cunneen was ill-fated from the start, ICAC Inspector David Levine has argued.

And he's warned more needs to be done to oversee the body which he says abused its powers in its pursuit of Ms Cunneen.

Mr Levine on Monday delivered a blistering attack against ICAC Commissioner Megan Latham after she claimed his assessment was fundamentally flawed.

"I welcome the opportunity to get a word in ... the word I wish to get in is 'debacle'," Mr Levine told the parliamentary inquiry examining his report.

Mr Levine said the Independent Commission Against Corruption had tried to exploit and abuse its powers while conducting Operation Hale in 2014.

This was done "on an absolutely unproved basis, to attack the reputation of a senior member of a legal profession in this state," he said.

No one "in their most vivid dreams or worst nightmare" would have envisaged that a car accident between Ms Cunneen's son's girlfriend and a pizza delivery driver would have led to "hearings in every court up to the highest court in the land," Mr Levine said.

He also lamented the saga which followed, saying it led to the most "demeaning bloodletting between the two major media groups in this country" and showed the watchdog had a "sullen resentment to oversight".

"Operation Hale especially points to the need of a strong oversight body which should at all times should be apprised of every matter that is being dealt with by the ICAC," Mr Levine said.

He said the NSW government would only be strong in its fight against corruption if it ensures the ICAC "is infected by nothing but the most honourable motives, the fairest of dealings and highest level of propriety in the conduct of its business".

Mr Levine said he bore Ms Latham no personal animosity but described her response to his report as extraordinary.

Ms Latham last month told the inquiry Mr Levine's report lacked proper factual foundation.

She also tabled the secret phone recordings that sparked the 2014 investigation which examined whether Ms Cunneen perverted the court of justice by allegedly giving her son's girlfriend advice to fake chest pains to avoid a breath test after a car accident.

Ms Cunneen has consistently denied the allegations and the High Court in April 2015 ruled the investigation did not fall within the scope of the ICAC's functions.

The parliamentary inquiry on Monday heard the cross-party committee had received legal advice that it could not publicly release the potentially explosive recordings.