Two cracks in the darkness, like stones thrown against a window.

That is how Gwen Winchester described the gunshots that killed her husband and ignited a legal storm that raged for 30 years.

Was it a mafia hit? It seemed logical. But the head of the ACT's police force had more than one enemy.

The mafia question lingered throughout media coverage, inquiries, and appeals. But both times the murder went to trial, it was former treasury official David Eastman sitting in the dock.

Mr Winchester was shot twice in the head as he got out of his car. ( ABC News )

In the middle of the summer holidays, on January 10, 1989, the day-night match between Australian and Pakistan was on TV, and Canberrans were settling in for a quiet night.

About 9:15pm, Australian Federal Police Assistant Commissioner for the ACT Colin Winchester pulled into his elderly neighbour's driveway — knowing she felt safer with a car in front of her home.

Mr Winchester was returning from visiting his brother to discuss an upcoming hunting trip, and as he parked, turned to pick up a box of bullets from the passenger seat.

Police believe the gunman was standing behind the unmarked police car as Mr Winchester opened the door and moved to get out.

The first bullet hit him in the back of the head, and he collapsed inside.

Within seconds the gunman stepped to the right and fired another shot to the side of Mr Winchester's head.

Two cracks were heard, a noisy car drove off. No one saw anything.

An instant investigation

Sorry, this video has expired Commander Lloyd Worthy speaks to the media the day after Colin Winchester was shot

Gwen Winchester initially thought her husband was playing a trick when she saw him slumped in the driver's seat. Then she saw the blood.

The investigation was one of the largest in the ACT's history. ( ABC News )

After rushing into the house to call the police, she went back outside.

"I just cuddled him," she would later say.

As police descended on the Winchesters' quiet street in the suburb of Deakin, the night turned frantic.

In the immediate aftermath, police closed roads and stopped more than 2,000 people to ask for their details.

More than 700 houses were doorknocked, motels were checked, and a special taskforce interviewed more than 1,200 people.

But even as police swung into action, the investigation was showing signs of fracture.

A hangover of unease and tension from the marriage of Canberra's original police force and the Australian Federal Police a decade earlier split investigators in two directions.

One group pursued the seemingly obvious theory that the mafia had killed Mr Winchester, while the other quickly focused on a retired public servant with a grudge against police.

Why David Eastman?

Sorry, this video has expired David Eastman is arrested by detectives in December 1992

Highly intelligent and just as stubborn, David Harold Eastman was in the frame almost from the start.

After graduating as dux of the prestigious Canberra Grammar school — an honour he shares with Gough Whitlam — the diplomat's son secured work in the Australian Public Service in the mid-1960s.

Despite taking time off to care for disabled family members, he rose quickly through the ranks of the APS.

But, as courts would later hear, he was hostile and difficult to work with.

He left his job at the Treasury Department in 1977, but engaged in several bitter disputes with the public service over the terms of his departure, eventually launching a protracted bid to return.

At the time of Colin Winchester's murder Mr Eastman was due to face court on assault charges, after punches were thrown during a fight with a neighbour over a car space.

Mr Eastman believed he should not have been charged, going so far as to meet with Mr Winchester and ask for his help to have the matter dropped.

On the morning of the killing, a letter arrived at Mr Eastman's flat reading that the police would not intervene.

The Crown would later argue Mr Eastman was infuriated, believing the charges could prevent him from re-entering the public service — a motive Mr Eastman's lawyers contested heavily.

The long lens of the law

When police came knocking the day after the assassination, David Eastman could not account for his movements the night before, saying only that he had been driving around, and "may have" bought take away food.

It later emerged that hours after the shooting Mr Eastman was in Fyshwick visiting a sex worker —a woman who went on to give evidence several times.

Eastman was under heavy surveillance by police throughout the early 1990s. ( ABC News )

She said in Mr Eastman's 2018 trial that he seemed completely normal, not stressed or anxious. She did not remember any mention of the shooting.

Within days of the murder, surveillance of Mr Eastman ramped up. He was followed to the beach in Narooma on the NSW South Coast, and officers would hide in camouflage at the National Botanic Gardens where he would regularly walk.

That was the soft surveillance.

Chief investigator Ric Ninness took a more robust approach, confronting Mr Eastman in public and asking him questions, after Mr Eastman told police he did not want to talk to them.

That method was based on advice from a psychiatrist who had suggested the two-pronged attack as a way to pressure him to crack.

It did not work, and nearly 30 years later Mr Eastman still protests his innocence.

David Eastman's flat was bugged and he was followed by police. ( ABC News )

Police also placed listening devices in the flat next door to Mr Eastman's.

It is on these tapes that prosecutors believe he confessed to the murder, allegedly muttering "had to kill him sitting down" and "he was the first man I ever killed".

But the quality of the tapes was so bad that Mr Eastman's lawyers said the word "killed" could just as easily have been the word "kissed".

The mafia theory

The major alternative theory on the murder can be traced back more than a decade earlier, to the killing of Griffith anti-drugs campaigner Donald Mackay.

Lead investigator Mr Ninness was on the scene of Mr Winchester's murder within half an hour of the shooting.

"Our first thoughts were the mafia of course," he later said.

The era was marked by fears about organised crime and its influence over drug crime in Australia.

It's thought police informant "You Know Who" led mafia figures to believe they had paid for Colin Winchester's protection. ( ABC News )

Colin Winchester had set up Operation Seville in the early 1980s, targeting mafia-linked marijuana crops at Bungendore in NSW, in the hope of finding information about Mr Mackay's murder.

He and other officers wanted to let the crops grow and begin to be distributed, hoping it would lead them to more senior members of the group.

Several people were eventually charged and were about to face court at the time Mr Winchester was shot.

The key witness, an informant dubbed "You Know Who", ultimately refused to give evidence, causing the case to crumble.

Some theorised Mr Winchester infuriated the mafia and was shot as payback. ( ABC News )

One theory was that mafia members killed Mr Winchester as payback after realising they were caught in a police trap.

The informant emphatically denied telling the group Mr Winchester was involved in the operation.

But David Eastman's lawyers produced a police transcript in which he admits he did.

Much of the information about the mafia theory was suppressed, or heard in closed court, meaning the full picture of what happened may never come to light.

The trial of David Eastman

David Eastman was charged over the killing in 1992, after a coronial inquest was re-opened and the coroner ordered his arrest.

Six years after the murder, Mr Eastman faced a chaotic first trial, where his behaviour in the courtroom was often the centre of attention.

A courtroom sketch of David Eastman (date unkown).

He would frequently disrupt the court with curse-riddled outbursts and he sacked his lawyers many times throughout the trial.

After one mid-trial blow up, Mr Eastman's bail was revoked.

He would not taste freedom for 19 years.

For the rest of the trial he watched proceedings on a television in a room under the court, with Judge Ken Carruthers able to control the volume if he tried to interject.

But that did not protect the court from Mr Eastman's outbursts during one stretch while he was representing himself.

Mr Eastman's trial was characterised by his outbursts and stunts. ( ABC News )

Justice Carruthers: Well, now do you have any questions by way of cross-examination of the witness? David Eastman: Yes, I would like to ask your honour why you are such a corrupt shit. ... David Eastman: I wish to ask your honour why you are such a lying c***. Justice Carruthers: Yes, well, I will treat that as a no.

Mr Eastman has since argued the trial should have been abandoned when his bail was revoked, so that his fitness to plead could be examined.

Instead the jury found him guilty and he was sentenced to life in prison.

But conviction was only the first chapter of Mr Eastman's fight.

In the years afterwards, he unsuccessfully mounted appeals and frequent legal bids to gain his freedom, then demanded an inquiry into his conviction.

A first inquiry found he was fit to stand trial in the case, but a second inquiry, ordered in 2012, was key to setting him free.

Free after 19 years

Sorry, this video has expired David Eastman freed from Canberra jail after murder conviction quashed ( Elizabeth Byrne )

When Justice Carruthers sentenced Mr Eastman to life in prison, he praised "one of the most skilled, sophisticated and determined forensic investigations in the history of criminal investigation in Australia".

If that had been true, Mr Eastman may never have faced a second trial.

The gun used to kill Colin Winchester was never found. But David Eastman can thank another gun, which may not have even existed, for his eventual freedom.

Fresh evidence was needed to launch the 2012 inquiry. This came in the form of an old friend, who claimed he had borrowed Mr Eastman's car to go rabbit shooting in 1985 or 1986.

That, lawyers said, could have explained gunshot residue in the car that helped put Mr Eastman away.

Ultimately, the witness was unreliable, with inquiry head Justice Brian Martin finding he was putting on a show.

But the inquiry went on to find serious deficiencies in forensic gunshot residue evidence used to convict David Eastman.

Justice Martin declared the trial had not been fair.

"In my view the substantial miscarriage of justice suffered by the applicant should not be allowed to stand uncorrected," he said.

As for the mafia theory, Justice Martin wrote a confidential chapter in his report, after two secret hearings, which he said canvassed new evidence.

All Justice Martin would say was that if that evidence had been available at the time of the original trial it may have helped Mr Eastman.

"Suspicion is generated, but it does not rise to the level of a positive hypothesis," he said.

David Eastman and his lawyers during his second trial in 2018. ( ABC News: Ian Cutmore )

Justice Martin recommended Mr Eastman's conviction be quashed, but suggested a retrial would not be feasible given the passage of time, and the number of witnesses that had died.

But a full bench of the ACT Supreme Court — which had the final say — disagreed, finding it was in the interests of justice to order a new trial.

Mr Eastman sought bail and was finally released in August 2014, amid a media frenzy.

But an instant shadow was cast over his new-found freedom.

Four years after Mr Eastman was released, he returned to the ACT Supreme Court to again answer charges he shot Mr Winchester — this time without the flawed forensic evidence.

After months of evidence and testimony, the jury on Thursday finally ended the justice system's 30-year pursuit of Mr Eastman with two words: not guilty.

A three-decade search for answers

Mr Winchester's killing remains one of the highest profile murders in Australian history.

In the AFP's magazine, Mr Winchester's police colleague Alan Mills described the assassination as "the end of the age of innocence in Australia".

Colin Winchester (R) left behind family and many friends. ( Supplied )

The day after the murder, then justice minister Michael Tate sat at a press conference next to AFP Commissioner Peter McAulay, who was on the verge of tears.

"For a senior police officer to be assassinated in the haven of his own home, in the driveway, off duty, is a new element in Australian criminal annals," Senator Tate said.

"For that reason, every resource has to be mustered to deal with it quickly."

Almost 30 years later, the debate still rages.

The trials of David Eastman may have ended on Thursday, but legal action had not. His compensation case against the ACT Government was pending, looking to make up for the 19 years he lost behind bars.

The question of who killed Colin Winchester became part of Canberra's DNA, and even with the verdict, many people will still argue the toss for years to come.

But on one level, the toll of the 30 year saga is clear: Mr Winchester's wife Gwen died two years ago, knowing she would never learn for certain who fired those two shots in the night.