Mark Perry was found not guilty by a jury in 2014 over the slaying 11 years earlier of Shane Chartres-Abbott in Reservoir.

It's been revealed Perry admitted his involvement to "Lawyer X" Nicola Gobbo while his solicitor Jim Valos took a phone call.

"Perry started telling me of his involvement," Ms Gobbo wrote in a statement, showed to a royal commission into police use of informers on Thursday.

She said Perry admitted to making arrangements for the killing as "retribution" for a rape. Chartres-Abbott was due to face the County Court on a rape charge the day he died.

But Ms Gobbo's unsigned and undated statement to police detailing the confession could have outed her as a police informer. The statement was never used at trial.

Detective Senior Sergeant Peter Trichias told the commission he didn't know about the confession. He agreed then-homicide squad boss Ron Iddles, who took the statement, would have discussed it with other investigating officers, but it's not clear whether it was taken higher up the chain.

Warren Shea and Evangelos Goussis stood trial with Perry and were also acquitted of both murder and manslaughter.

Meanwhile, the identities of some of Melbourne's gangland snitches will be kept secret after judges ordered their names continue to be protected.

Crooks who turned on fellow criminals to get shorter jail sentences at the height of the city's gangland wars have long been protected by suppression orders preventing them being named or identified.

Commissioner Margaret McMurdo applied to identify five individuals in the hearings, worried the inquiry would otherwise be hindered.

Police objected, citing concerns for safety of the individuals and their families.

Three Court of Appeal judges agreed to allowing the people to be named in closed hearings, but they rejected an attempt by some media to lift all protections.

Earlier on Thursday, Victoria Police Commissioner Graham Ashton defended the force - which has been blamed for tardiness providing evidence to the commission - against multiple complaints.

"I know we've been regularly criticised for slowness. The complexity of the task is enormous," he told 3AW.

More than 100 officers are working on the inquiry and, between staffing and legal costs, the top officer estimated a cost of about $1.5 million a month.

Over 18 months, he anticipated a bill as high as $27 million.

Police are also appearing in appeals by some of Ms Gobbo's former clients.

Jailed getaway driver Faruk Orman, convicted over the underworld slaying of Victor Pierce, has been granted an appeal.

Convicted drug traffickers Tony Mokbel, Rob Karam and Zlate Cvetanovski are also seeking leave to appeal.

Australian Associated Press