Victoria Police are assessing a slew of new leads in the 20-year unsolved case of an Armaguard truck robbed at gunpoint by a fake road crew.

It was a highly organised and audacious daylight heist that netted thieves $2.4 million and, when pulled off in 1994, was Australia’s biggest armed robbery.

There is now “optimism” police are close to cracking the 20-year cold case.

A re-activated investigation is focused on Queensland, far from suburban Melbourne where a fake roadwork crew robbed an Armaguard truck at gunpoint 20 years ago.

“There is no doubt it was a well planned crime – the setting up of the road block, acquiring of road cutting instruments, the witches hats, and the clothing the offenders wore to stop the van,” Victoria Police detective acting inspector Mark Caulfield told AAP on Wednesday.

“It’s certainly an investigation that is very, very active at the moment and there is a sense of optimism there.”

In March, police announced they had charged an unnamed Melbourne lawyer with allegedly attempting to launder some of the stolen cash.

Detectives also searched a rural property near Port Douglas, taking items for forensic examination, and Insp Caulfield said more property searches were planned.

Police have also called for public help to find a distinctive tradesman’s utility used in the robbery, and then likely dumped at a North Cairns wreckers and onsold.

The early model Dodge or Bedford has metal storage compartments on its tray.

Detectives are also working to identify a man and woman seen in security footage visiting a Melbourne bank with some of the stolen cash in 1994.

“One of those individuals, we think, lives in Queensland at the moment,” Insp Caulfield said.

It was the recent offer of a $100,000 reward by Armaguard that generated a slew of new leads.

“At the time it was the largest armed robbery in Australia,” Insp Caulfield said.

“People that might have been too scared to come forward 20 years ago might be quite prepared to come forward now.”