Police linked to the murder investigation of two colleagues used improper evidentiary and disclosure practices, Victoria's anti-corruption watchdog has found.
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 the Melbourne suburb of Moorabbin in 1998 while patrolling potential restaurant robbery targets.
A number of statements made by important witnesses were never included in the prosecution brief or disclosed at trial, IBAC found.
IBAC Commissioner Robert Redlich QC said the shocking deaths of the officers 22 years ago devastated their families and colleagues.
"As with any police investigation, this significant murder investigation demanded that police discharge their obligations and perform their duties fairly, impartially and always according to the law," he said in a statement.
"Any failure to do so imperils the sound administration of justice, as well as impacting community confidence in police and the criminal justice system."
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 officer in armed robbery and homicide squads in the late 1990s and early 2000s.
The commission began its probe into how the police conducted the investigation in November 2017 and public hearings followed.
IBAC did not re-investigate these 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 Robert. 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 deeply concerning that IBAC found a variety of improper evidentiary and disclosure practices were employed and it is surprising that, historically, some officers were even taught these practices at the Victoria Police Academy. Victoria Police advises that this is no longer the case," the commissioner said.
"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."
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.