A damning royal commission report by Queensland judge Margaret McMurdo found the gangland barrister's dual role as lawyer and informer over nearly two decades had compromised convictions, while officers corrupted the criminal justice system

"It is a grave thing when a lawyer loses their ethical bearings and betrays their clients and the administration of justice," she wrote in a more than 1000-page report.

"It is even more shocking when police officers who are sworn to uphold and enforce the law enable conduct the Court of Appeal ... recently considered 'might prove to be one of the greatest scandals of our time in relation to the workings of the criminal justice system'."

The affair cost Victoria Police $64 million while the royal commission itself - initially allocated $7.5 million - is expected to come in under its $39.5 million final budget.

Victoria Police commissioner Shane Patton admitted it was a huge cost to the organisation that would impose "significant" financial constraints."

"There could also be civil litigation - it's another hurdle to determine who picks up that bill," he told Melbourne's 3AW radio.

Ms McMurdo found that 1011 people may have had their criminal cases affected by the improper informer relationship.

Two people have had convictions overturned, more appeals are underway and potentially many more to come, she said.

In an apology described by the commissioner as "belated", Mr Patton blamed the organisation's structure and processes at the time.

But Ms McMurdo said if it was flawed it was because individuals, particularly senior leaders, "lacked the moral clarity, vision and ability to fix those flaws".

She identified failures by top ranked police including ex-commissioners Simon Overland and Graham Ashton, as well as gangland-busting Purana Taskforce bosses Jim O'Brien and Gavan Ryan, and detective Stuart Bateson.

Mr Patton said some officers remained in senior positions. No-one has been stood down.

"We'll have to take time to look at the report. It's also complicated by the appointment of the special investigator," he said, noting the need to determine if there's admissible evidence against them.

Ms McMurdo highlighted the fairness of the process they face.

"If the DPP determines that it is in the public interest to prosecute, those charged will receive a fair trial according to law, unlike those whose trials were corrupted by their conduct," she said.

Mr Patton has also promised to comply with Victoria Police's obligations to hand over evidence to appeal courts.

In her closing remarks Ms McMurdo blasted their delays, saying she was concerned about the slowness with which the force had provided people with information they should have received years earlier.

She recommended the force start reporting monthly on their disclosure progress.

Victorian Attorney-General Jill Hennessy said all the recommendations from Ms McMurdo's report would be adopted, with work to begin immediately.

Victoria Police has established Taskforce Reset, led by Deputy Commissioner Wendy Steendam, to oversee the process.

Australian Associated Press