Drug kingpin Williams, murdered in his cell in 2010, had long been thought to be behind Kinniburgh's murder, along with a string of others. He had agreed to give information about other murders to police at the time he was killed.

Alleged underworld hitman Stephen John Asling is charged with Kinniburgh's 2003 murder.

In 2008, two years before he died, Carl Williams had spent more than a week locked in talks with detective sergeant Sol Solomon to put together a statement on the Terrence and Christine Hodson murders - one of the most high-profile unsolved murder investigations in the gangland war.

During that time, he talked extensively about the death of Kinniburgh, but that statement was never completed because of his murder. Five pages of notes were taken. Mr Solomon read a small section to court on Tuesday:

"Stephen Asling and Terry Blewitt are the shooters. Blewitt is now dead. He — that is Carl Williams — provided the firearms and procured the homicide, and will need an indemnity. He also said he has further knowledge which he is willing to provide at a later time."

Williams had long-denied involvement in Mr Kinniburgh's death, telling Fairfax Media "My conscience is clear."

He was later granted indemnity from prosecution. Police planned to take a full sworn statement from him about Mr Kinniburgh's murder after the Hodson matter had been dealt with.

Mr Solomon said he had met with Mr Williams several times at Barwon Prison, where he was in custody.

During their first meetings he was non-committal, but later agreed to assist police in return for indemnity over the brutal murder of the Hodsons, who were both police informants.

Asling and Blewitt weren't the only suspects in the investigation. It was revealed in court that police had witness statements indicating that Mick Gatto - who was close to Kinniburgh - believed hitman Andrew Veniamin and Carl Williams had been involved in Mr Kinniburgh's killing, not Mr Asling.

Police later excluded Mr Veniamin as a suspect. Mr Gatto later shot and killed Veniamin. He was charged but acquitted of murder on grounds of self-defence.

Kinniburgh, 63, had parked his car and was walking to his two-storey Kew house on December 13, 2003, when he was gunned down.

He was a lifelong friend of Judy Moran and her former husband Lewis. Mick Gatto was a pallbearer at his funeral.

Kinniburgh was considered an influential standover man. He had convictions for dishonesty, bribery, possession of firearms, resisting arrest and assaulting police.

In 2002, a coroner implicated Kinniburgh and Jason Moran in the 1998 death of gangster Alphonse Gangitano.

Mr Asling's committal hearing, to decide if he will stand trial for murder, continues.

With Steve Butcher and Nino Bucci