David Harold Eastman has now spent 6895 days, or 18 years and 10 months, in custody for one of the nation’s most notorious police killings.

A jury convicted Eastman after hearing an “overwhelming” circumstantial case that he shot dead the ACT region’s police chief, Assistant Commissioner Colin Stanley Winchester, in 1989, as he sat in his car in his neighbour’s driveway.

He has always professed his innocence, and has launched a string of legal battles to try and clear his name.

The latest bid, the Eastman inquiry, came to a close on Thursday afternoon, following months of evidence, argument, and, this week, closing submissions.

Mark Griffin, QC, who is representing Eastman, used the final moments of his closing submission to urge inquiry head Acting Justice Brian Martin to finally remedy what may have been “great injustice”.

“You can make a report to the full court that corrects the record… and that makes a conclusive finding that there was a miscarriage of justice,” Mr Griffin said.

He said the possibility of a re-trial of Eastman 20 years later would be “so remote as to not be contemplated”.

The inquiry has covered a vast, often dizzying volume of material since it began taking evidence late last year.

The most shocking revelations to emerge have concerned the gunshot residue analysis that linked Eastman to the murder scene.

The credibility of the work of Victorian-based forensic expert Robert Collins Barnes has been savaged, and glaring deficiencies identified.

The Director of Public Prosecutions and the Australian Federal Police have argued that, even without Barnes’ forensic work, there was an overwhelming circumstantial case against Eastman.

The remaining evidence includes a motive, an inability to explain his whereabouts, his threats against police and Mr Winchester, efforts to secure a gun, identification evidence, and, potentially, confessional utterances made in his home.

But Mr Griffin says the forensics was closely interwoven with the other evidence, and was a “pervasive theme” in the prosecution’s lengthy and damning closing submission to the jury in Eastman’s 1995 trial.

He said evidence suggesting an alternate hypothesis for the killing, involving Italian organised crime figures, should act as a counterweight to the remaining case against Eastman.

Questions have also been raised about the conduct of investigation police, and their alleged harassment of Eastman.

Mr Griffin described the behaviour as “brutish” and outside of the law, something he said Acting justice Martin could not let stand.

He said the harassment was designed to force Eastman to say something stupid in his bugged home.

Concerns have also been raised about the prosecution’s compliance with their duty to disclose certain information to Eastman’s defence team.

Mr Griffin also used his closing submission to argue his client’s fitness was not properly considered at the trial.

He also said there were questions of apprehended bias concerning the trial judge, Acting Justice Ken Carruthers.

The inquiry has continued on in the shadow of a challenge to the very order that created it, launched by the Director of Public Prosecutions.

That challenge has been heard in the ACT Supreme Court, which has reserved its decision.

The inquiry was allowed to push on taking evidence while the challenge was resolved.

Acting Justice Martin ended the inquiry by publicly thanking everyone involved, describing the work of counsel assisting Liesl Chapman, SC, and her junior Duncan Berents as “remarkable”.

He spoke directly to Eastman, who is listening in to the inquiry, thanking him for not disrupting the progress of the inquiry.

The judge told the inmate that his counsel had done an “excellent job” representing his interests.

He noted that history meant it was likely Eastman had tensions and disputes with his counsel, and that the inmate may have thought he could have done a better job at times.

But Acting Justice Martin said it was important for Eastman to know Mr Griffin had represented his interests in the “very best way possible”.

The judge will now prepare his report and hand it to the registrar of the Supreme Court.

It is unknown when and if it will be published.

The report will come before the full court, who will then decide on the next course of action.