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Christopher Dawson murdered his wife in January 1982 because he was so tortured at the thought of losing his teenage lover, a judge has found.

In an almost five-hour judgment read to two packed courtrooms on Tuesday, Justice Ian Harrison found Dawson guilty of murder - concluding a 40-year-old mystery and leading to jubilant applause and cheering from those listening.

"I am left in no doubt. I am satisfied beyond reasonable doubt that the only rational inference (is that) Lynette Dawson died on or about 8 January 1982 as a result of conscious or voluntary act committed by Christopher Dawson," the NSW Supreme Court judge said.

The former PE teacher was "so distressed, frustrated and ultimately overwhelmed" that he could not have an unfettered relationship with his teenage babysitter, known as JC, that he plotted to kill his wife and install his young lover in his family home days after the murder.

Justice Harrison rejected the possibility Mrs Dawson abandoned her husband and children to vanish without a trace from their home on Sydney's northern beaches.

"The proposition is ludicrous," he said.

Mrs Dawson had a strong attachment to her daughters and had remained steadfastly committed to her husband even as her marriage crumbled around her.

Addressing the media outside court, Greg Simms said his sister's name had been cleared, and that she had been betrayed by a man she loved. But she was still missing.

"We would ask Chris Dawson to find it in himself to finally do the decent thing and allow us to bring Lyn home to peaceful rest," he said.

Hedley Thomas, the journalist behind The Australian's Teacher's Pet podcast on Mrs Dawson's disappearance, said he felt privileged to be able to help in the way that he could.

"Her story struck me as so unjust, so unfair at the time," he said.

He criticised the original police investigation for not taking proper action initially, saying that Dawson should have been charged 40 years ago.

"He has had 40 years of his life that he has been able to enjoy without any accountability. That's disgraceful."

Paul and Peter Dawson refused to comment on their brother's conviction, swearing at TV cameras as they left the court.

Despite the case being wholly circumstantial, without a body or murder weapon, Justice Harrison found there was no other reasonable hypothesis for the disappearance other than murder given Dawson's growing obsession with JC prior to the killing and how quickly she had been installed in his home.

JC and the former Newtown Jets rugby league player eventually married in 1984 and separated in 1990.

The babysitter's evidence was mostly truthful and reliable, Justice Harrison said, rejecting Dawson's allegations she had been corrupted by an acrimonious custody battle between them.

However, claims by JC that Dawson had driven her somewhere in 1981 to find a "hitman" to kill his wife were dismissed as improbable.

Justice Harrison dismissed claims Mrs Dawson had been seen alive after January 1982 as fabrications, unreliable or too vague to be of any worth. He also rejected claims by Dawson that he had been contacted by his wife after her disappearance as outright lies.

Dawson was previously a man of good character and there was no evidence he had been physically or verbally violent towards his wife before the murder.

Some evidence of allegedly violent incidents witnessed by friends and neighbours were rejected as being infected by the publicity surround the case.

This included through The Teacher's Pet podcast with Thomas speaking to individuals who would become crucial witnesses in the case and contaminating their memories by revealing what others had said.

The judge called the original police investigation into what happened "lackadaisical" and "arguably less than perfect" but said Dawson had not pointed to any significant disadvantage he had suffered because of the delay.

Dawson will apply for bail on Thursday, pending a sentence hearing. It is not known whether he will appeal the verdict.

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Christopher Dawson murdered his wife in January 1982 because he was so tortured at the thought of losing his teenage lover, a judge has found.

In an almost six-hour judgment read to two packed courtrooms on Tuesday, Justice Ian Harrison found Dawson guilty of murder, concluding a 40 year old mystery.

"I am left in no doubt. I am satisfied beyond reasonable doubt that the only rational inference (is that) Lynette Dawson died on or about 8 January 1982 as a result of conscious or voluntary act committed by Christopher Dawson," the judge said.

Earlier in the NSW Supreme Court, Justice Harrison rejected the possibility Mrs Dawson abandoned her husband and children to vanish without a trace.

He also dismissed claims Mrs Dawson had been seen alive after January 1982 or that she had contacted her husband.

"The whole of the circumstantial evidence satisfies me that Lynette Dawson is dead, that she died on or about 8 January 1982 and that she did not voluntarily abandon her home," he judge said.

Mrs Dawson had a strong attachment to her husband and daughters, was no "shrinking violet", and had limited funds to support herself. This led the judge to completely reject the proposition she had abandoned the home with only the clothes on her back.

"The proposition is ludicrous," the judge said.

The keenly awaited judgment was delivered seven weeks after a lengthy trial in which Dawson, now 74, was accused of murdering his wife and disposing of her body so the then-teacher could have an unfettered relationship with his former student and babysitter, JC.

Mrs Dawson's body has never been found.

In his reasons, Justice Harrison found that Dawson lied about phone calls he allegedly received from his wife after her disappearance.

The judge also rejected any sightings of Mrs Dawson alive and well after January 1982 as either fabrications, unreliable, frail or vague.

"None of the alleged sightings were genuine sightings of Lynette Dawson," he said.

Evidence by JC that Dawson had driven up to Southwest Rocks to pick her up from a holiday on January 11, 1982 was accepted by the court.

"Lyn's gone. She's not coming back. Come back to Sydney and help me look after the children and be with me," Dawson said to JC over the phone before he drove up from Sydney to collect her.

JC's evidence was mostly truthful and reliable, Justice Harrison said in rejecting allegations by Dawson that she had been corrupted by an acrimonious custody battle between them.

JC and the former Newtown Jets rugby league player married in 1984 and separated in 1990.

However, Justice Harrison dismissed claims by JC that Dawson had driven her somewhere in 1981 while she was still in high school to find a "hitman" to kill his wife.

It was improbable Dawson would have told a young impressionable JC of this alleged plan at the time, the judge said.

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© AAP 2022

A Melbourne videogame developer has made an audio-only game for vision impaired people, featuring some specifically Australian sounds.

Sounds, Hidden to be Found, made by Allison Walker and Rebecca Dilella, enables players to catch cicadas, explore drains, and talk to birds, feeling their way in the game using sound only.

"It's about exploring your neighbourhood and listening to things, finding new places and hearing how the sound changes," Walker told AAP.

She recorded the sound effects herself and included bird sounds from Cornell University's Macaulay Library, a comprehensive online collection of the noises of the natural world.

Unusually for an audio-only game, players can move and explore the landscape in three dimensions, with no limitations on their movement.

Walker, who is sighted, found it challenging to play the game herself, and considers it a prototype from which more complex narrative games could be developed in future.

Audio games began to be produced as early as the 1980s, primarily by coders who were themselves blind and found visual games inaccessible.

But things are changing rapidly, according to US-based video game industry accessibility consultant Brandon Cole, with mainstream games that incorporate the needs of vision impaired players, and a range of audio-only games on the market.

For starters, there's Blind Drive - which Cole describes as hilarious, The Vale: Shadow of the Crown, and Manamon, which he believes is the vision impaired person's answer to Pokemon.

Cole, who is totally blind, told AAP that video game accessibility is important for many people with disabilities.

"Video games are the one of the greatest mediums for escapism, because not only do they allow you to experience a story the same way a book or a movie would... you get to play those characters and interact with that world," he told AAP.

Cole tests out different games to advise on how user friendly they are, and says vision impaired gamers need all information necessary to play the game to be provided entirely through audio cues.

While Cole grew up patiently playing his way through mainstream games that weren't designed with his needs in mind, he said some younger blind gamers have grown up with audio-only, although whether these are in fact better is a question of taste.

He said mainstream developers are listening more when he talks about game accessibility, and audio-only games are one branch of a burgeoning number of options.

"There's a lot on the horizon, the future is bright for accessible gaming, it really is," he said.

Sounds, Hidden to be Found was funded with a Film Victoria grant.

© AAP 2022