Former Victorian detective Charlie Bezzina has told an anti-corruption hearing into the murders of two police officers two decades ago that it was common practice for members of the homicide squad to sign backdated witness statements.

Key points: Bandali Debs and Jason Roberts were convicted of murdering Sergeant Silk and Senior Constable Miller in Moorabbin in 1998

Bandali Debs and Jason Roberts were convicted of murdering Sergeant Silk and Senior Constable Miller in Moorabbin in 1998 IBAC is examining the emergence of two conflicting statements by an officer who comforted Senior Constable Miller as he died

IBAC is examining the emergence of two conflicting statements by an officer who comforted Senior Constable Miller as he died The hearing is focused on alleged police misconduct rather than the soundness of the convictions of Debs and Roberts

The Independent Broad-based Anti-corruption Commission (IBAC) is examining the conduct of police investigating the 1998 killings of Sergeant Gary Silk and Senior Constable Rodney Miller and whether the statements of officers who were there on the night were doctored.

The commission heard police investigating the murders were allegedly asked to leave out crucial descriptions of the offenders given by Senior Constable Miller as he lay dying in a Moorabbin street.

The corruption watchdog is examining the emergence of two conflicting statements by Senior Constable Glenn Pullin who comforted the dying policeman — one that makes no mention of more than one gunman and another that does.

Mr Bezzina told the hearing he was unaware of Senior Constable Miller's last words until recently, despite signing the two statements which are both dated August 16, 1998.

Gary Silk (left) and Rodney Miller were shot and killed in Moorabbin in 1998. ( ABC News )

Under questioning from counsel assisting the commission, Jack Rush QC, Mr Bezzina conceded he had acted improperly by "unwittingly" signing the second statement around two years later, agreeing there was no legitimate excuse.

"In hindsight yes, I've got to accept it and I make no excuses for it," he said.

When asked if the original version had been altered to put some "meat on the bones" of Senior Constable Pullin's statement, Mr Bezzina said he would "not have a bar of that because I would have understood the enormity of doing that and potentially perverting the course of justice".

Mr Bezzina told the hearing it was common practice for members of the homicide squad to sign backdated statements.

The IBAC heard another policeman at the scene of the murders, Senior Constable Graham Thwaites, was "upset" his statement was "ripped to shreds" by Detective Grant Kelly, who told him not to include a description of the offenders.

Mr Bezzina said he had heard of police excluding descriptions of suspects in witness statements but he did not condone the practice.

"It's unacceptable to my level," he said.

"It's my way to put everything in a statement and leave a court to decide what's admissible."

Jason Roberts claimed he was not there on the night the two officers were murdered. ( AAP: Julian Smith )

Yesterday, Mr Rush said the investigation had uncovered evidence indicating a "pattern of systemic behaviour by Victoria Police in statement-taking that is of such gravity that it has the potential to pervert the course of justice".

He told the IBAC the disclosure to the defence of all relevant material is fundamental to a fair trial.

"The use of such practices by police not only impacts on the integrity of the police investigation, but has the very real potential in trial circumstances to amount to a perversion of the course of justice," Mr Rush said.

Bandali Debs and Jason Roberts were convicted of murdering the policemen in 2002, but Roberts claims he is innocent and is trying to make a Supreme Court plea for mercy.