The enigma is about how and why a defendant was not shown possibly exculpatory material in the possession of police and prosecutors before his trial.

Eastman was not told about critical evidence that might have helped him. A judicial inquiry, under Justice Brian Martin, found that this failure was inadvertent, but that it nonetheless deprived Eastman of a fair trial and made his conviction a miscarriage of justice. Now Eastman is in court arguing that the failure was not inadvertent, but deliberate misconduct, warranting an order that the new trial be permanently stayed. Justice David Ashley is considering the argument, if in guarded terms for fear, apparently, of prejudicing potential jurors should the trial proceed. [On which account a good deal of previously public material has suddenly, if without actual public explanation, been removed from open access records.].

The riddle is why other potentially exculpatory material which emerged after his conviction was not drawn to defence or public attention until quite recently. It was withheld from last year's public inquiry – the Martin inquiry – although it was plainly material to its purpose.

That's a question going beyond the conduct of a particular prosecution team, and particular set of investigators. It goes to the attitude, approaches and policies of both the AFP and the ACT prosecution system. It has the potential to suggest that some ACT police and prosecutors are more interested in covering up their institutional mistakes than in promoting justice.

David Eastman was convicted in 1994 of the murder, with a silenced rifle, of AFP Assistant Commissioner Colin Winchester in January 1989. He has always denied his guilt, and been in continuous appeals, ancillary litigation and inquiries ever since – all fiercely resisted by the AFP and the DPP. Last year Justice Brian Martin recommended the quashing of Eastman's conviction, after finding that Eastman had been denied a fair trial. The leading forensic witness, Robert Barnes, a Victoria Police forensic technician, was fundamentally discredited. The defence was not told of doubts, held by overseas experts, of Barnes' work and conclusions.

The inquiry findings led to further litigation. Ultimately the Supreme Court ordered that Eastman face a fresh trial. But that order had the effect of further delaying any official inquiry or review into how the AFP and the DPP had, for 20 years, sat on new information about the case, and sought simply to obstruct any attempt to reopen it. It also indicated a massive resistance to any sort of external criticism.

During the 1994 trial, the prosecution stressed that the work of Barnes had received the thumbs up from the FBI and other international forensic experts. It was not as clear-cut as that, but Eastman did not know.

FBI scientist Roger Martz was one of a number of forensic investigators whose work was heavily criticised by an FBI whistleblower in about 1995, soon after he gave evidence in Canberra. This led to an inquiry into deficiencies in the FBI investigation of major US terrorism cases. The allegations against Martz were familiar ones to those used to seeing the modern flourishing and glorification of scientific evidence. Martz was said to have lost detachment, and to have become the advocate and player for the prosecution team rather than the independent scientist. He was said to be poor in his record-keeping. He was said to venture well outside his field of expertise, and to become defensive and dogmatic about conclusions, once formed.

The FBI review was completed in 1997. Soon police and prosecutors around the US were being notified that the FBI no longer stood by the evidence a score of their experts had given in court cases over the years. Government lawyers and detectives were invited to review prosecutions which had depended on this "expert" evidence, and, if necessary to drop cases, organise fresh trials or, perhaps have forensic work redone. The review led to many convicted Americans being released once it was realised that the prosecution cases had become tenuous.

The report itself was not publicly issued until a few years ago. It is possible, however, that copies of the report came into Australian hands 19 years ago. It was certainly in official hands in Australia 16 years ago.

In 2000, the US Department of Justice had remembered that other countries, as well as US states and counties had successfully sought help from the FBI. It was not sure that these countries had been notified in 1997 that the FBI now disavowed some of its experts.

Copies of the adverse report were sent to the AFP and the Commonwealth DPP. Letters referred to FBI evidence in the Eastman trial and asked if the outcome might be affected if it were known that the FBI was now disavowing its expert.

No one here seemed interested. The AFP, apparently, filed the report away without taking any action. We don't know whether the Commonwealth DPP's office made any further inquiries, passed the report to the ACT DPP or wrote back to the US Department.

Eastman was by now aware that Barnes had been under suspension for scientific misconduct by the Victorian Police before his trial. But he was not told that there was new information undermining Barnes' evidence. Indeed, police and the DPP were denying in appeals and other litigation that there were any doubts about the case.

At some stage, perhaps immediately after the trial, the AFP had taken the position that Eastman had been rightly convicted. It saw no point or profit involved in following any further investigative leads the case had provided, or new tips that came in. Even less was it interested in any information pointing away from Eastman. Tips or other information were simply filed away, unactioned.

The AFP has long been criticised for the fact that it did not conduct any post-trial review of its investigation. It is, indeed, even now in denial about stringent criticism of its competence, detachment and personnel from judges, lawyers, and other police, and by Justice Martin. It is simply trying to brazen it out, arguing that it cannot investigate itself while a criminal trial may be pending.

Dead silence from Canberra after 2000 prompted the US Justice Department to try again, five years later. This time we know the report reached the ACT DPP, headed then by Richard Refshauge, now a judge of the ACT Supreme Court. Refshauge sought advice from the AFP. The FBI was sent transcripts of the Eastman trial, and documentation of the work done by Barnes and Martz. The FBI found the old files, and, after some delay reported that if the work had been done as suggested by the worksheets, its conclusions fell within Martz's field of competence.

Refshauge was already wondering if Eastman should be told, but, once he received this report, seems to have decided not to tell him. His decision, then, might be criticised or supported. What is much more curious is why the report, and the correspondence with the US Department of Justice, was not disclosed by the DPP's office last year during the Martin inquiry. It did not emerge until quite recently.

This underscores a big problem encountered by Justice Martin. The DPP office appeared not to go to the inquiry seeking to be of help, or as a participant in a fair-minded inquiry about Eastman's guilt. It seemed to go as an interested party, determined to defend its people, its actions and its reputation. It tried continually to rein in, or close down the inquiry. On repeated occasions counsel assisting the inquiry complained of a lack of co-operation from the DPP's office, and about the slowness, and reluctance of the DPP and AFP in producing documents associated with the murder investigation. No new evidence was presented, no help volunteered.

The Martin inquiry was closely focused on the reliability of Barnes. The reliability of Martz was not in the terms of reference. This might excuse a failure to volunteer the US Department of Justice report, but is hardly consistent with claims of a completely clear prosecution conscience.

The AFP also indicated that it had adopted a policy at the Martin inquiry of defending the verdict and the investigators, not in evaluating any new material. It passively co-operated, but without enthusiasm or initiative. Evidence of its "file and forget" approach to new evidence emerged only by accident. Martin was to find that one recent tip, said to record an admission of involvement in the murder, made by a very senior Calabrian crime figure to a Victoria Police informant, was ignored as a matter of policy. Had it been properly investigated, it could have supported an alternative theory of who did the murder.

The adverse Martin inquiry findings produced a burst of AFP activity, at DPP behest, to see what could be done, in the modern day, to bolster its original brief against Eastman. What new evidence will be offered is not known; police and prosecutors have repeatedly missed deadlines about producing evidence on which they plan to rely.

But the new brief, apparently, will include an array of "propensity evidence" by which the prosecution will reprise the well-remembered fact that Eastman, when in florid mental disturbance was given to ringing, abusing and threatening journalists, officials, and others he thought had crossed him (including me). This evidence, it will be suggested, shows Eastman was of violent disposition.

Yet such evidence cuts in different ways. None those made subject to his rages, some more profound and longer lasting than the animus he is said to have had towards Winchester, ended up dead. Or, as in my case, even very frightened. I have heard more threatening, unwelcome and abusive calls from politicians and public servants.

Once before the trial, Eastman said some menacing words on the telephone to one of my children. Angry, though not personally frightened, I rang a police contact to ask if there were any particular bees in Eastman's bonnet that night. My contact said he would check with the listening-in squad. Soon after he rang back to say that there was no particular reason for alarm; that Eastman had been ringing in sequence and abusing about 20 or 30 different people. There did not seem to be any special agitation about me. Perhaps the speculative transcriptions of thousands of hours of low-quality tape recordings, tendered at trial by the prosecution in unconvincing demonstration of claimed admissions, might equally be used by the defence to demonstrate a then mental illness that was apparent to all but the police, prosecution and trial judge, and a large gathering of conflicts and molehill mountains on many fronts.

Be that as it may, the management and conduct of the investigation by the AFP, the ACT DPP, and, after a while the ACT Attorney-General and his department seems to them a matter for history, of no interest or consequence to the broader community. From the point of view of very interested parties that is. Examination, it will be said, must wait until court proceedings against Eastman are over, whether from a stay, or a verdict.

Until that day, it seems, there will be no general police introspection about criticisms made of the original investigation, and investigators. Nor will there be any sort of external review to see whether the AFP can or will learn from the matter. But even if the AFP do not see how they could benefit from such a review, members of the public (or ACT citizens who pay the AFP top dollar for a fairly humdrum service) might think otherwise.

Likewise, the ACT government can use a pending trial to defer any investigation into how it supervised, then ignored for two decades, what even the ACT Supreme Court now, all too belatedly, agrees to have been a serious miscarriage of justice.

The AFP has not, since its formation in 1979, been the subject of general external critical review, other than friendly ones conducted by people of its own nomination. The closest to a general review, into the Haneef "terrorism" fiasco, was scathing, but produced no systemic or lasting change.

All detectives actually involved in the Winchester investigation have retired. Most of the lawyers in the 1994 trial have become judges, or retired, or both. It is hardly surprising, or sinister, that some of them, being cross-examined this week about what they did, or why, simply cannot recall, or are put to positing what they probably did, or might have done. Even if police and prosecutors can locate sufficient witnesses to present a survivors' case, it will require high art, and a lot of co-operation, to present evidence in a way fair to all sides, the prosecution as much as the defence.