The truth behind the notorious mafia shooting murder of aspiring Liberal politician Don Mackay in the 1970s appears to have been taken to the grave, after the man who likely pulled the trigger died this week.

Who was James Bazley: The man known as "Machine Gun" was a convicted hitman

The man known as "Machine Gun" was a convicted hitman He was also believed to be the last living person to know details about the mafia murder of Donald Mackay

He was also believed to be the last living person to know details about the mafia murder of Donald Mackay Bazley is believed to have shot Mr Mackay in 1977, although this was never tested in court

James Frederick Bazley, who was also known as "Iceman" or "Machine Gun", is long believed to be the hitman who gunned down the prominent anti-drugs campaigner in Griffith, NSW, in 1977.

Mr Mackay's demise remains Australia's pre-eminent mafia murder mystery, and has gripped the nation for four decades.

Mr Bazley, who was in his 90s, died a free man in a Melbourne nursing home this week, but he was no stranger to prison.

In 1986 he was sentenced to nine years behind bars for conspiracy to murder Mr Mackay — but he was never tried over actually firing the gun used to kill the father of three.

He was also handed a life sentence for his role in the double murder of drug couriers Isabel and Douglas Wilson, whose bodies were found in 1979.

Mackay unsuccessfully contested the state seat of Murrumbidgee in the elections of 1973 and 1976. ( www.australianmissingpersonsregister.com )

However, Mr Bazley walked out of prison in 2001.

He has been described by police as someone who saw murder as a job and felt no remorse.

Despite many searches for Mr Mackay's remains, Mr Bazley kept his lips sealed until the end.

Retired police officer Brian McVicar worked on the case during his time with the NSW Drug Squad in the 1970s.

He said it was difficult to get people to talk about Mr Mackay's murder, even after a $200,000 reward was offered in 2013.

"There was a lot of money offered in the past and nothing ever came out from that, but the information has always been fairly tight with the Victorian connections and it's taken a long time to get to this stage and maybe there will be closure," he said.

Mr McVicar said he was optimistic Mr Bazley's death would prompt people who know details of the murder to come forward.

"Over the years there's been a clairvoyant, there's been information and different theories about what happened, this could be a good one … let's hope for the family of Donald Mackay … I'm sort of hopeful myself," he said.

James Bazley was given half the usual sentence as a judge took his age into consideration. ( ABC News )

Crimes 'of the worst kind'

Mr Bazley was known as a violent and hardened felon, with a judge once describing his crimes as "of the worst kind".

He was believed to be the last living person who knew the ins and outs of Australia's first political assassination.

Mr Mackay paid with his life for blowing the whistle on the Calabrian mafia — also known as the 'Ndrangheta — and their escalating marijuana trade in regional NSW.

The monument in Griffith which stands in honour of Donald Mackay. ( Supplied: Monuments Australia )

The then-43-year-old vanished from the car park of the Griffith Hotel after having drinks with friends on July 15, 1977.

Police found three bullet casings and a smearing of blood on the door of his van.

However, his body has never been found.

His disappearance triggered one of the country's biggest police investigations, with 3,500 people interviewed.

It also sparked the Woodward Royal Commission into the illegal drug trade in NSW, which found the 'Ndrangheta ordered a hitman to take out Mr Mackay.

Mr Mackay had informed the police of a large marijuana crop in nearby Coleambally, which led to four convictions.

For this, police believe mafia godfather Tony Sergi sanctioned Mr Mackay's murder.

Known as the "Don of Dons", Mr Sergi died a year ago on Thursday without ever being charged.