Australia’s most notorious rotten cop, Roger Rogerson, is a person of interest in a decades-old underworld murder mystery that police hope a $1 million reward will finally help solve.

Detectives believe Robert “Jack” Richardson was shot dead execution-style on March 4, 1984, the day before he was due to go to trial over a heroin trafficking conspiracy.

Twenty-seven days later, fishermen found his body at Strath Creek in central Victoria dumped in bushland off King Parrot Creek Road.

A senior police officer had last spotted Richardson at a now-defunct ice cream parlour in Acland Street, St Kilda in the early hours of March 4 where, far from looking scared, he appeared relaxed and comfortable with two unknown men.

“(Richardson) knew his way around; he was very street smart and we are confident he would not have hopped into a vehicle and travelled to Strath Creek if he felt he was at risk of harm or injury,” homicide squad detective Inspector Dean Thomas said.

“It very much feels to investigators he’d been lured out there … by a number of people.”

Police believe Richardson, 49, who was on bail and living with his girlfriend in St Kilda before his death, was killed two years to the day after they made their first arrests over the heroin trafficking racket.

That was no coincidence, Det Insp Thomas said.

The inquiry had deep links to one of Australia’s most infamous underworld crimes, the cold case shooting of undercover NSW police operative Mick Drury.

Richardson’s co-accused in the trial was Alan Williams, a member of Melbourne’s infamous Painters and Dockers union, which police say was connected to their probe involving a high-level organised crime syndicate.

Corrupt cop turned killer Rogerson was acquitted over the 1984 attempt on Drury’s life but along with long-missing hitman Christopher Dale “Rent-a-Kill” Flannery, is still suspected of plotting the hit at Williams’ behest.

Flannery is considered most likely to have fired the bullets through the kitchen window of Drury’s Chatswood home that struck him in the chest, although it’s also been speculated he and Melbourne triggerman Laurie Prendergast habitually traded contracts from interstate to avert suspicion.

Drury was a prosecution witness in the case against Richardson, Williams and their co-accused Brian Hansen.

Rogerson was among a number of people of interest in the Richardson case, Det Insp Thomas confirmed on Tuesday.

“There’s been communication with Roger Rogerson and there’s been communication with a number of different people throughout this investigation,” he said.

Police have collected fresh DNA and say they have received more information since the original inquiries into who was behind Jack Richardson’s murder.

However, they have insufficient evidence to charge anyone.

Richardson was popular among family, friends and associates and had a relatively minor criminal history, Det Insp Thomas said.

At the time of his death, he had a young daughter who had grown up not knowing who killed her father and why.

“Given Jack’s significant criminal history and associations, we also believe there is a strong likelihood people with information were afraid to come forward at the time of his death because they feared significant retribution,” Det Insp Thomas said.

“We’re hoping some of those people may now be able to speak to us without those fears or concerns.”

The $1m reward will be paid at the discretion of the chief commissioner of police for information leading to the apprehension and conviction of the person or people responsible.

The director of public prosecutions will consider granting indemnity to anyone who leads them to the perpetrators.

Jack Richardson’s demise was dramatised in the 1995 ABC miniseries Blue Murder based on the life and times of Rogerson and Sydney underworld heavy Arthur “Neddy” Smith. His role was played by Wolf Creek star John Jarratt.