Investigations into potential criminal activity at one of the country's biggest consulting firms could take years to complete.
Police are looking into allegations former PwC partner Peter Collins illegally shared tax policy information he had access to under a federal government contract.
Australian Federal Police commissioner Reece Kershaw told a Senate estimates hearing on Friday investigating such matters was challenging due to their complexity and the availability of resources.
He said he knew some detectives who spent eight to 10 years investigating large companies.
"We have to resource these matters appropriately," Mr Kershaw said.
"We have to go long range and sometimes we have to wear criticism for taking our time ... we're up against some really heavy firepower from those companies.
"It's a very challenging environment for us to operate in, however I have every confidence in the team that's going to be undertaking this investigation."
The Australian Taxation Office first sought advice from the police fraud and anti-corruption team in 2018, which Mr Kershaw said was standard practice for complex tax matters.
However, based on the documents provided by the ATO, there was not enough information for police to make an assessment about formally referring the matter for a criminal investigation.
Deputy Commissioner Ian McCartney said then-home affairs minister Peter Dutton was not briefed on the interaction with the ATO.
"Within the AFP we have a set guideline on ministerial briefings and this wouldn't be a reason to brief the minister," he said.
"It (wasn't) a referral for investigation, ATO were seeking advice on this matter."
Mr Kershaw said the AFP did not receive a criminal report for PwC to be investigated until 2023.
"An investigation is under way, it is complex (and) we expect we will have to triage thousands of documents," he said.
"We will need to navigate various legal considerations in relation to these documents."
The AFP has faced criticism for perceived conflicts of interests with the embattled consultancy firm.
It has ended all its contracts with PwC due to the ongoing criminal investigation.
AFP chief financial officer Paul Wood said federal police previously had nine contracts with PwC before they were ended on June 30.
"Some (contracts) were partially complete and essentially they handed over what they had done at that point in time and we only agreed to pay a percentage of those contracts," he said.
"In my correspondence to PwC and in my conversations, I referred to a perceived conflict of interest and just demonstrating a (need for a) clean break."
The fallout from the scandal has been felt across federal and state governments in their engagements with external consultants.
The NSW parliament is considering law changes which would result in million-dollar penalties for private consultants who leak confidential government tax information or cover up breaches by their colleagues.
