The NSW Independent Commission Against Corruption has had to revise how it approaches investigations and not pursue some others due to a lack of resources.
A parliamentary committee has also heard that the auditor-general who advised ICAC should be funded by the parliament and not the government has not received a response to a report tabled 18 months ago.
ICAC chief commissioner Peter Hall QC told a budget estimates hearing the key performance indicators for the commission had been revised down and reports were being delayed.
ICAC conducted complex investigations that could take an extended period of time, he said.
"Those engaged in corrupt conduct do not leave paper trails and they destroy any material to show what happened," Mr Hall told the hearing on Thursday.
"We're not going to take the word of a single person on matters whereby an adverse finding could result, so it does take time."
Mr Hall said ICAC would be better placed to handle its workload if it was given the additional staff it had sought.
Labor's Penny Sharpe asked if that meant some cases of corrupt conduct would be overlooked.
"It means that some matters have to be parked," Mr Hall said.
"It means that matters that we would have pursued we just simply can't afford to spend time and resources on because there are other matters of a complex nature which are sucking up the resources, particularly where there are multiple people involved."
Auditor-General Margaret Crawford was asked to provide advice to the government on funding for ICAC.
Government funding of ICAC posed a threat to its independence and it has been suggested that the parliament should determine the commission's funding and not the executive government.
"It is regrettable in the extreme that the auditor-general's report was delivered and tabled in October 2020 ... and yet we're here still in a position where nothing material has happened," Mr Hall said.
Ms Crawford said she received a cabinet in confidence letter from Premier Dominic Perrottet in February and responded in March, asking that her response be on the public record.
"My response in general terms, certainly as (Mr Hall) has just said, commented that the proposal would improve transparency of the process, but did not go far enough to resolve the threats to the independence of agencies that were raised in my audit report," Ms Crawford said before tabling her response.
She said no reply has been provided at this stage.
