A tangle of ambition, jealousy and intrigue has riven Australia's second-biggest police force as it emerged that senior figures conspired to overthrow the Chief Commissioner and replace her with a “puppet”.

An inquiry that uncovered the plot also exposed an alleged tip-off to a detective that he was being secretly investigated for murder in a series of leaks intended to undermine the head of the Victorian state police force and frustrate her reforms.

Christine Nixon, the country's only woman police chief, said yesterday that she felt betrayed after evidence gathered through phone intercepts established that Paul Mullett, the police union boss, planned to install Noel Ashby, a former assistant commissioner, as his pawn. “He has always been an ambitious man,” Ms Nixon said of Mr Ashby. “Perhaps I should have done something about that, but ambition is not an offence.”

Mr Mullett, Mr Ashby and Stephen Linnell, the former media director, now face possible criminal charges over the leaks that compromised the 2003 murder investigation, which could land them in jail for up to 25 years. Ms Nixon said yesterday that she believed they would be charged.

The report by the Office of Police Integrity accused the men of engaging in betrayal, collusion, deceit and abuse of authority to topple Ms Nixon and her deputy. “Sworn police with obligations to uphold the law were exposed as individuals prepared to thwart the efforts of other police who were discharging their duties in investigating serious crimes,” it said.

The report came after six days of open hearings last November. The Chief Commissioner is said to have infuriated Mr Mullett, known as “The Fish”, with her drive to modernise the force of 13,600 officers. The report said that without the “behind-the-scenes manoeuvring”, Ms Nixon would now be in a better position to pursue strategic reform. “The corruption exposed at such a senior level of the police stood as a significant barrier of the reform agenda,” it said.

Mr Mullett, who says he will fight the allegations, is described in the report as a forceful, even intimidating character who rose through the ranks from major crime and armed robbery units. He is one of only two Victorian police to receive two decorations for valour. “I may not be an angel, your honour, but I pride myself as being a police officer who hates crooks,” he told the inquiry in November.

Ms Nixon said that she believed most of her officers were honest and “now we can get on with business”.

Victorian police have been tainted by alleged links to brutal gangland killings of 28 mobsters between 1998 and 2006. Allegations of corruption have also forced the closure of the drug and armed offenders squads.

The scandals have prompted calls for a Royal Commission to investigate beyond the police force, along the lines of inquiries in the Eighties and Nineties that established institutionalised corruption in New South Wales and Queensland.

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