A retired senior Victorian judge unknowingly offered to review Victoria Police's use of supersnitch Nicola Gobbo a decade ago.
Frank Vincent, a Supreme Court justice for more than 20 years, was approached by decorated former deputy police chief Sir Ken Jones in 2010 over concerns about serious wrongdoing within Victoria Police.
Sir Ken has revealed he did not use names but told Mr Vincent of wrongdoing which had "undermined, in a very profound way, the Victorian criminal justice system over some years".
The retired deputy commissioner first learned Ms Gobbo was a police informer in 2009.
After learning more, including that she had dobbed on clients, he approached Mr Vincent in 2010 about leading a judicial review into the matter.
Sir Ken said Mr Vincent was open to the idea but it never went ahead because it would require sign-off from then chief commissioner Simon Overland.
But he believed Mr Overland, who he had learned was involved in the use of Ms Gobbo as an informer, had questions to answer about the scandal and was "conflicted".
Instead Sir Ken made a formal approach to the state ombudsman, telling the inquiry on Friday he made seven or eight reports.
"I was doing what I could," he said.
Sir Ken was scathing about the use of Ms Gobbo as an informer.
"It began as highly irregular and unethical and deteriorated over a period of years to illegal and chaotic," he said.
He blamed a "toxic" culture of loyalty to "the hierarchy above all else" and cosiness between the force and its independent corruption watchdog, the Office of Police Integrity.
"We wouldn't be sitting here today if Victoria Police was effectively regulated," he said.
Sir Ken believes he was sidelined within the force after separating the organisations in 2009.
Sir Ken also believes his speaking up about Ms Gobbo cost him his career.
He was sacked by Mr Overland in 2011 and investigated for leaking sensitive police information.
He was later cleared of the allegations.
"I was humiliated and my hard won, decades-old professional reputation was destroyed in an instant," he wrote in his statement.
He told the inquiry it was "disgusting" what he and his wife had been put through.
"I am in no doubt this detrimental action was taken because it was suspected that I had reported what I found out about Nicola Gobbo and other matters and that I needed to be discredited and silenced," he said.
Sir Ken moved back to the UK after his firing but told the inquiry he continued to speak to the ombudsman about his concerns around Ms Gobbo.
Mr Overland is set to give evidence to the inquiry from Monday.
Australian Associated Press