The future of Victoria's police watchdog is uncertain after the collapse of a high-profile perjury case against former police assistant commissioner Noel Ashby.
A technical legal error allowed Mr Ashby to become the second senior police figure to beat serious perjury charges brought against them by the Office of Police Integrity (OPI).
Tuesday's development followed the collapse of the perjury case against former police union secretary Paul Mullett last year, which was part of the same investigation.
The collapse of Mr Ashby's case was the "final nail" in the coffin of the OPI, Mr Mullett said on Tuesday.
Former police media director Stephen Linnell will lodge an appeal on Wednesday to quash his perjury conviction - after pleading guilty last year - his barrister Ron Gipp says.
Mr Mullett, Mr Ashby and Linnell are also considering suing for compensation over damage to their reputations and careers.
Mr Ashby told AAP he did not want to comment on his plans until three other summary charges against him were also dropped, which is expected to happen this week.
Mr Ashby, whose trial was due to start this month, walked free on Tuesday when prosecutor Chris Ryan, SC, announced the crown would not pursue the case.
Justice Robert Osborn then found Mr Ashby not guilty.
The transcripts of the OPI's 2007 public hearings involving Mr Ashby, Mr Mullett and Linnell have now been ruled inadmissible, wasting millions of taxpayer dollars.
Justice Osborn last week ruled that then OPI director George Brouwer didn't properly legally empower former Federal Court judge Murray Wilcox, QC, to run the 2007 hearings and take legal oaths.
OPI director Michael Strong said he had been assured the error had not happened in any other case.
The OPI had accused Mr Mullett, Mr Ashby and Linnell of leaking confidential information that tipped off former Detective Peter Lalor he was being investigated over the murder of gigolo Shane Chartres-Abbott.
Mr Wilcox ruled in 2007 that although no "smoking gun" showed Mr Mullett directly passed information about the murder probe to Mr Lalor, it was logical to think that he did so.
Mr Mullett said Tuesday's court ruling brought into question the "incompetent" management of the Victorian police force and the OPI.
He called on Victorian Premier John Brumby to immediately establish a public inquiry.
"There are a number of issues that should be addressed and can only be addressed by an open public inquiry, a fair inquiry," he said.
Mr Strong defended the body's record in investigating police corruption and described the operation as a success despite Tuesday's decision.
"We operate in a highly regulated legal environment, could there really be a clearer example?" he told reporters.
"The damage to Mr Ashby's reputation has been the result of his conduct exposed by the OPI, which led inevitably to his resignation from Victoria Police.
"The setback for the OPI doesn't negate the OPI's proven record of strengthening ethical and professional standards in Victorian policing ... 31 parliamentary reports, hundreds of recommendations, most of them accepted by Victoria Police."
Victorian police chief Simon Overland said he was disappointed the charges won't be determined in court.
He defended the need for a police oversight body but said whether that was the current OPI or not was a matter for the government.
Police Association secretary Greg Davies accused the OPI of clutching at straws in defending its record.
The Victorian opposition has renewed calls for an independent anti-corruption commission.
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