The Independent Broad-based Anti-corruption Commission tabled a special report on Friday to state parliament on its investigation into the murders of Sergeant Gary Silk and Senior Constable Rodney Miller.

Sgt Silk and Sen Const Miller were fatally shot in Moorabbin in 1998 while patrolling potential restaurant robbery targets.

Multiple statements made by important witnesses were never included in the prosecution brief or disclosed at trial, IBAC found.

The commission found improper witness statement-taking practices were evident in the Lorimer Taskforce, during the investigation of the 1998 murders, and were also used by some officers in armed robbery and homicide squads in the late 1990s and early 2000s.

The commission began its probe into the police investigation in November 2017 and public hearings followed.

IBAC did not re-investigate the murders or seek to establish if the two people convicted received a fair trial.

At a 2002 trial, it was argued there were two killers - Bandali Debs and his criminal sidekick, 22-year-old Jason Roberts. Both were convicted and jailed for life.

Roberts has always maintained his innocence and had a second appeal heard on the grounds of fresh evidence.

Police had been accused of deliberately manipulating evidence about the number of offenders at the scene, including in a statement from Senior Constable Glenn Pullin, who noted Sen Const Miller's dying declarations.

The anti-corruption watchdog remains concerned the improper practices identified are still used by some officers.

"It is surprising that, historically, some officers were even taught these practices at the Victoria Police Academy," IBAC Commissioner Robert Redlich QC said.

"Victoria Police advises that this is no longer the case.

"Because Victoria Police has never clearly called out and stopped such improper practices, IBAC has found there is a real risk that these practices continue to be used by some police today."

A response to the report from Victoria Police says there is "insufficient evidence" to find some practices were ongoing or widespread, and none of the practices are taught to new recruits at the academy.

Further, police said it was not possible to determine the extent or prevalence of such practices within the squads in the late 1990s or within the force generally during any time period.

"IBAC should not find that these practices were or remain widespread, commonplace or entrenched within Victoria Police," statement reads.

IBAC has recommended Victoria Police strengthen its evidentiary and disclosure practices and advise the commission how it will effectively embed the required standards into its policies, procedures, training, and importantly, practice.

The state government has also been recommended to introduce a statutory obligation of disclosure, to reinforce the common law duty.

Australian Associated Press