Previous investigations wouldn't stop it re-investigating the relationship between Victoria Police and gangland informer Nicola Gobbo, Commissioner Robert Redlich says.

In a 2015 report, Murray Kellam found there had been "negligence of a high order" in Victoria Police's use of Ms Gobbo as a super snitch.

The final report of a royal commission into the informer relationship - due to be handed down next month - won't recommend Ms Gobbo or a number of senior police face criminal charges for their actions.

Instead commissioner Margaret McMurdo says that's a decision for prosecutors.

Her decision has prompted questions about who would investigate, given that role would ordinarily fall to Victoria Police.

Anti-corruption watchdog IBAC has been suggested as an alternative investigative body.

Doug Drummond, who investigated corruption within Queensland Police as a special prosecutor, has called for a similar process in this case.

He suggested IBAC was not appropriate because it had already decided police did not engage in criminal conduct.

But in a response released on Tuesday, Mr Redlich rejected that claim.

He said the findings had to be considered in light of information available at the time, and that on that "limited evidence" he couldn't conclude officers had intended to pervert the course of justice.

Mr Redlich noted it was Mr Kellam's findings that had ultimately led to Ms Gobbo's public exposure as an informer, and to the royal commission.

Whichever body investigates next will have an "extensive body" of evidence to examine in determining if charges should be laid, he said.

Australian Associated Press