Assistant Commissioner (Crime) Steve Fontana said he will offer short-term contracts to ex-detectives when their specific knowledge was needed to compile evidence in unsolved murder cases.

Last month he recruited the former head of the Briars Taskforce, retired Detective Inspector Steve Waddell, to prepare the coronial brief of evidence into the gangland murder of nightclub bouncer George Germanos, shot dead in an Armadale park 15 years ago.

The ambush of Germanos has been linked to three other murders and a series of armed robberies carried out in Melbourne over 20 years.

The central figure to the Ocean's Eleven-style crime gang is underworld identity Bob "Bluey" Mather, who died of natural causes in 2014.

Police believe Mather ordered Germanos' murder because the bouncer bashed his son outside a St Kilda nightclub the previous year.

Mather and members of the Oceans Eleven gang have been linked to the 1999 murder of crime figure Dimitrios Belias and the 1984 killing of Werribee mother Maryanna Lanciana. Both were shot in the back of the head at point-blank range.

Two years ago police announced a collective $3 million reward for information into the three murders. "We have information the three murders are connected and there will be people in the community who have associated with a particularly criminal group with information that can assist us," the then head of the homicide squad, Detective Inspector John Potter said.

Mather has also been linked to the killing of Shane Chartres-Abbott, the so-called vampire gigolo prostitute shot dead in 2003.

Waddell's Briars Taskforce was set up to investigate the Chartres-Abbott murder. The alleged hitman who confessed to the murder and three other men was acquitted of the crime.

The Briars Taskforce was told Mather was pivotal in organising the hit on Chartres-Abbott.

Before he died police visited Mather and told him he was likely to be charged with three murders.

Assistant Commissioner Fontana said Waddell had been employed to prepare the Germanos brief of evidence because he had a detailed knowledge of the case "and was aware of what material should be highlighted''.

"It will be a more efficient process than having someone who has not worked on the cases have to prepare from the ground up."

Mr Fontana said he believed more former police could be used on short-term contracts so their particular expertise would not be wasted.

Former Chief Commissioner Ken Lay has advocated the use of retired police in specialist areas. His 2025 blue paper on the future of policing concluded senior officers should, "Harness the skills and experience of former police members by bringing them back on a part- or full-time contractual basis ...  for example former detectives could work on cold-case investigations."