A "conscious and deliberate" act to help police secure a conviction, or a legitimate decision to exclude evidence that was deemed unreliable?

Those are the key questions that a judge will consider as he determines whether two former officers attempted to pervert the course of justice in their handling of a 40-year-old murder.

Alan Hall spent 17 years in prison for the 1985 murder of Arthur Easton.

He was later exonerated by the Supreme Court, which found a significant miscarriage of justice had occurred.

Now the former officers, who have name suppression, are facing charges over their role in Hall's conviction.

Lawyers made their closing arguments in the High Court at Auckland on Thursday.

On 13 October 1985, Arthur Easton and his teenage sons, Brendan and Kim, were at home when one heard an intruder in their home.

Crown prosecutor John Billington KC recounted what happened next.

"There was a fight and in the course of that fight Mr Easton was fatally wounded and Brendan Easton was seriously wounded. The offender escaped by leaving the home through a hedge into a walkway and made his way down Alma Crescent to Shirley Crescent and close to Clevedon Road."

Later that night, a man called Ronald Turner phoned the Papakura Police Station to reported seeing a hooded Māori man running across Clevedon Road around the time of the attack.

His description tallied with what the Easton brothers had told police in their 111 call - that they were attacked by a six-foot-tall Māori man wielding a bayonet.

Although the brothers would later cast doubt on their recollection, two further witnesses also described seeing a man of a similar description.

"Mr Hall, by reason of his ownership of a bayonet and a hat found at the scene was interviewed on 11 December, 1985. He gave a number of explanations as to why the bayonet and hat were not in his possession on the night of the murder. He was also questioned in relation to his ownership of a blue sweatshirt which was similar to that seen by Mr Turner," Billington said.

"Now obviously, Mr Hall did not match the description given by Mr Turner. Mr Hall is a Pākehā, somewhere close to five-foot-eight in height, frail build and clearly not Māori."

Billington questioned why police only presented some of Ronald Turner's evidence to the jury at Alan Hall's trial, excluding his description of the offender's ethnicity.

And why did the former officers not provide his original statement to Hall's defence team when they requested all relevant evidence?

"By modifying the Crown case, the defendants denied the defence lawyers, the trial judge, the jury, the Court of Appeal access to the prior statements.

"They each carried out an act which was intended to and had the obvious effect of preventing the courts from doing justice."

John Billington said it was difficult to accept that their conduct was anything but "conscious and deliberate".

But defence lawyer David Jones, KC, said police had "very real concerns" about Turner's recollection of the man he saw.

"What someone says in a statement to a police is not evidence. It is a statement they have made which could or could not be used as evidence in the case," he said.

"That has to go through a filtering process. And that is exactly what happened here."

Furthermore, Jones said, it was ultimately for the Crown to decide on what evidence was admissible in court.

"What we have is a recreation of events by the Crown which is castling a sinister light on an investigation which is carried out in an entirely normal and logical and legal way.

Jones urged Justice Gault not to rely on the findings of the Supreme Court when it quashed Alan Hall's conviction in 2022 because, he argued, the Crown had "capitulated" during the appeal.

Acting for the second defendant, Paul Wicks, KC, said there was no statutory framework guaranteeing pre-trial disclosure in the mid-1980s, as there is today.

"The Crown in this case has endeavoured to weave a few loose threads into a tapestry of guilt working backwards from the Supreme Court judgement," he said.

"It has failed, in my submission, to establish to the required standard that [the former officer] acted with any intention to pervert the course of justice and ultimately the only correct and safe verdict is one of not guilty."

Justice Gault reserved his decision.