Eastman became a free man in 2014, after 19 years behind bars.

A cohort of embittered and angry federal police officers believe he should not have been acquitted and remain fiercely protective of their organisation's investigation.

Even after so many years, the cauldron of emotions around this famous case - the cold-blooded assassination of our highest ranking public official - continue to steam and roil.

What's left amid the wreckage of people's lives and reputations, and hundreds of thousands of wasted dollars in court costs, is a void; a whodunnit and a murder mystery for the ages. So if Eastman didn't do it, then who did?

Former NSW independent MP John Hatton, now retired, said that it was not too late "to hold those responsible accountable".

The fiercely outspoken Hatton, whose tireless campaign against NSW police corruption in the mid-1990s led to the establishment of the Wood Royal Commission, said there was enough public concern and interest in this now-unresolved case to have an external, independent inquiry.

"The public have to make up their mind whether to protect Winchester's reputation, or dismiss the Mafia involvement altogether," Hatton said.

He described Eastman as the "perfect fall-guy" for the police case and maintains that "fear was a major factor in the way the investigation was skewed".

"I have no doubt there were credible threats made to police officers and their families," Hatton said.

"As a result, those lines of inquiry which didn't fit were discredited."

While he made enemies within state and federal police as a result of his anti-corruption campaign during his 23 years in the NSW Parliament, many of the dishonest practices and misconduct Hatton had alleged were fully exposed by the Royal Commission. Hundreds of NSW officers were compelled to resign in the wake of the far-reaching inquiry.

In re-examining the Winchester case, he said that "honest police have everything to gain and nothing to lose from an external inquiry".

We trawled The Canberra Times archives, including the reams of copy produced by the late Rod Campbell, our highly respected court reporter, to explore the most common Winchester conspiracy theory, the professional Mafia "hit".

As Campbell originally noted in his lengthy assessment of this theory 29 years ago, "the history of the Mafia in Australia is marked by extreme violence and assassinations".

In the wake of the Eastman acquittal, the organised crime reprisal theory now holds the strongest credence, yet it, too, is peppered by inconsistencies.

The Mafia, and more specifically a Calabrian group known as the L'Onorata Societa (honoured society), are touted as a likely candidate.

This notorious group is strongly suspected, but has never been fully proved, to have ordered the 1977 murder of anti-drugs campaigner Donald McKay.

So why would the Mafia order a hit on a high-ranking police officer in a Deakin driveway? Surely logic suggests that such a heinous public crime would only serve to unite and intensively focus police efforts in finding the killer?

The underlying chain of logic to the Mafia conspiracy, which reads like a Peter Temple novel, goes something like this:

From around 1980, federal police and the NSW Bureau of Criminal Intelligence had a well-placed informant cultivating cannabis in large scale plantations just outside Bungendore.

Known as Operation Seville, the police intention with this elaborate set-up was to use the drugs and their informant's distribution connections to nab Australia's Mafia bosses red-handed.

An important context to this theory was the uncertain relationship between two different police forces.

The federal police, with Winchester as their lead officer, were itching to crack a big drug case with international connections and had the resources to make it happen. But a critical weakness was that they were operating inside NSW territory. That meant the feds didn't have full visibility on NSW police information-sharing.

As the Wood Royal Commission uncovered some years later, the ranks of the NSW Police were then rife with widespread bribery, corruption, and evidence tampering.

At least three police-monitored and -controlled cannabis crops were harvested from Bungendore between 1981 and 1983 in order to embed the informant and his drugs supply into the criminal distribution network, setting the stage for a big police raid to come. The first crop, about 90kg, hit the streets of Sydney under police surveillance. Tens of millions of dollars were now at stake, and Australia's biggest drug kingpins were in the sights.

That's when it all went horribly wrong. And it's where the popular Mafia hit theory diverges on several different tangents.

One tangent - given the later damning outcomes of the Wood Royal Commission - is that corrupt members of the NSW Police who grafted significant sums of money from Mafia-run operations found out about the next big delivery and passed that information on to their criminal connections.

On three separate occasions, armed men came to the plantation and ripped off various quantities. In the final visit, they took around 5000 cannabis plants worth about $2.5 million.

Hundreds of police hours invested in a carefully constructed operation then went down the gurgler.

The National Crime Authority later launched its own investigation. NSW and federal police were embarrassed but exonerated by the revelations that followed.

What is unknown but speculated is that Winchester then secretively set about building evidence that would directly implicate NSW police involvement in the botched operation. Such activity would inevitably attract dire enemies within and without the NSW force.

Attempting to identify who pulled the trigger produces yet another odd tangent.

A meticulous reporter, Rod Campbell was always curious about the strange contrast between the professional methodology of the murder - two bullets at close range to the head - and the choice of firearm, a .22 calibre Ruger self-loading rifle.

It was this unusually prosaic weapon - far more likely to be used for hunting rabbits than as a weapon of choice by a cold-blooded professional hitman - that provided the prosecution's link back to Eastman, whom the prosecution claimed purchased a rifle of this exact type prior to the incident.

Further dismantling the colourful Mafia hit theory is the lengthy passage of time - five years - that elapsed between the botched Bungendore joint police operation and the timing of the Winchester shooting.

If the intention was to garner massive public attention and, in doing so, effectively silence others intending to provide evidence, it makes little sense that a planned prominent "hit" would be so long in its gestation.

Finally, the experienced investigators assigned to the case chased down every possible lead but could find no credible evidence, at least nothing that could stand up in court, to firmly link the Calabrians to the shooting.

And so the mystery deepens.