David Eastman, the former Treasury official jailed for Australia’s highest-profile police murder, is a free man for the time being.

Nineteen years into his life sentence for the murder of Australian Federal Police assistant commissioner Colin Winchester, Eastman’s conviction has been quashed.

Whether he has to face a new trial is now in the hands of the Director of Public Prosecutions.

Intriguingly, at the end of his 1995 trial, Eastman, now 68, was facing some 200 other charges of assault, threats and harassing behaviour.

None of them has been finalised.

In Australia’s sometimes turbulent history, many police officers have been murdered. The most notable perpetrator, Ned Kelly, became a folklore hero and a national icon of sorts.

The murder of Winchester electrified the nation, following a succession of royal commissions that uncovered the extent organised crime had intruded into the Australian community.

He was shot dead as he drove up the driveway of his suburban Canberra home about 9.15pm on January 10, 1989. The killer calmly fired two shots into Winchester’s head at close range while the commissioner sat in his car.

There was no shortage of suspects.

Winchester had been active in investigating crime groups operating in the cannabis business around the ACT.

Immediate speculation centred on a mafia hit, specifically by the Calabrian-organised crime syndicate Ndrangheta which was active in Canberra and Griffith.

But police inquiries speedily centred on Eastman, an abrasive loner with a paranoid personality disorder, a former Treasury official who had quit the public service then waged a long campaign to get his job back.

At the 1995 trial the prosecution claimed Eastman’s motive was concern that a conviction for a pending assault charge would bar his long-sought return to the public service.

Among those he lobbied was Winchester.

The prosecution said the final straw was a letter from Winchester which arrived on the morning of the murder, rejecting his representations and saying the assault matter would have to go to court.

The trial was marked by constant disruptions as Eastman sacked and rehired lawyers, sought adjournments and abused the judge and his own legal team.

The prosecution case was circumstantial.

Eastman made no admissions but neither did he have an alibi for the time of the murder.

Interviewed the next day – only because of his meeting with Winchester on December 16, 1988 – he said it was his evening habit to drive around and dine on takeaways.

A witness described a car like Eastman’s vehicle near the murder scene.

The murder weapon was never found but police did narrow it down to a particular .22 calibre American-made Ruger 10/22 rifle sold shortly before the murder by a Queanbeyan gun dealer.

A witness identified Eastman at the dealer’s home.

Because of Eastman’s revolving-door legal representation, the alternative hypothesis of mafia involvement was never seriously put to the jury.

Eastman’s trial ran from May 2 to November 3, 1995. He was sentenced to life imprisonment which in the ACT is indeterminate with no minimum period.

Eastman was never going to serve out his time quietly and even after exhausting all appeal avenues, pressed for a review of his case.

That finally came in September 2012, with former Northern Territory chief justice Brian Martin appointed to examine how the trial was conducted.

Reporting in May 2014, Martin’s conclusion there had been a miscarriage of justice, centred on tiny particles of gunshot residue from Eastman’s car boot.

A Victorian police forensic scientist had testified they were consistent with those found at the murder scene.

Justice Martin said the evidence, fundamental to the prosecution case linking Eastman to the murder scene, lacked any scientific basis and was deeply flawed.

Unknown to the defence, the witness was far from independent and objective.

He regarded himself as a police witness and was biased accordingly, Martin’s detailed report said.

Because a fresh trial was not possible after so long, he recommended the conviction be quashed and Eastman be granted a pardon.

However, he said he still thought Eastman committed the crime because even without the forensic scientist’s evidence, there was a strong but not overwhelming case.

“While I am fairly certain that the applicant is guilty of the murder of the deceased, a nagging doubt remains,” Martin said.

The full bench of the ACT Supreme Court was of a similar view.

In recommending a re-trial on Friday, the judges said the community had a vital interest in ensuring that a person against whom a strong circumstantial case for murder of a very senior police officer existed did not escape having a jury decide whether or not he was guilty of that crime.

“In our opinion it is not in the interests of justice for the controversy as to his alleged role in the murder to be left unresolved when there remains a strong circumstantial case against him,” they said.