After more than 40 years, decades of police investigations, two coronial inquests, nine weeks of evidence in the NSW Supreme Court, Chris Dawson is about to learn his fate.

Justice Ian Harrison will soon hand down his judgment following Australia's murder trial of the century.

His decision will go some way to answering the question – what happened to Lynette Dawson in the summer of 1982?

Ms Dawson, a 33-year-old mother-of-two and nurse, vanished without a trace from Sydney's northern beaches.

Her body has never been found and police "proof of life" checks failed to uncover any signs she was alive following a phone call with her mother on the evening of January 8, 1982.

Neither has she since contacted any of her friends or family, including her daughters.

Mr Dawson, a 73-year-old former teacher, pleaded not guilty to her murder.

Chris Dawson is awaiting judgment having pleaded not guilty to his wife's murder. Photo / NCA NewsWire

He has argued that Lynette chose to abandon their home after he had cheated on her and run off with a former student, who can only be known as JC.

However, the Crown prosecution has claimed he was "besotted" and "infatuated" with the 17-year-old and killed Ms Dawson so he could pursue a relationship with the couple's former babysitter.

The prosecution case has been entirely circumstantial and relied on a tapestry of evidence which they say pointed to Mr Dawson having had the motivation to kills his wife and dispose of her body.

January 9, 1982 and the Northbridge baths

On the evening of Friday, January 8, 1982, Lynette Dawson spoke to her mother Helena Simms on the phone.

Ms Simms was a prolific letter writer and chronicled her life in a meticulous diary, excerpts of which were tendered to the court.

In a diary entry dated January 8, Ms Simms wrote: "Rang Lyn, sounded half sozzled, said all was well."

Lynette Dawson's body has never been found. Photo / Supplied

Within hours, Lynette Dawson would be missing, never to speak to anyone again.

The prosecution has alleged that Ms Dawson was murdered on the evening of January 8, or some time the next morning.

Mr Dawson did not give evidence during his trial, with his defence instead relying on statements he had made during a police interview and calls which were intercepted by phone taps.

According to Mr Dawson, on the Friday night, he fixed his wife a glass of wine and he was upbeat about the prospects of resolving their problems.

Earlier that day they had been to marriage counselling and he said they left hand-in-hand.

"I remember we were going to have a honeymoon party, a celebration after coming from marriage guidance … so it was supposed to be a sexy celebration," he told police in 1991.

According to Mr Dawson, he dropped his wife off at a Mona Vale bus stop on the Saturday morning and she was to go shopping at the city markets.

It was planned that they would meet in the afternoon at the Northbridge Baths, where Mr Dawson worked a part-time job as a lifeguard.

He said that during his shift, a teenager who worked at the counter handed him the phone having answered a long-distance call.

On the other end was his wife who informed him that she needed time away, according to Mr Dawson.

Chris and Lynette Dawson, before her disappearance in 1982. Photo / Supplied

Lynette's mother and Phillip Day, a family friend, were also present at the baths.

In a letter to Lynette's sister on January 21, 1982, Ms Simms said: "I was with Chris at Northbridge Pool when he had the first call + he was obviously very much affected and emotional."

On February 18 1982, Mr Dawson reported his wife missing when he went to Mona Vale Police Station.

And on March 27 – the day following his wedding anniversary – he placed a notice in The Daily Telegraph: "Lyn, I love you, we all miss you. Please ring. We want you home, Chris."

'Like a rag doll'

A series of witnesses testified that they either saw, or were told of, incidents of Mr Dawson being aggressive or violent towards Lynette before her disappearance.

Mr Dawson's barrister Pauline David has said those allegations were disputed and argued those witnesses were either mistaken or embellishing their evidence.

Roslyn McLoughlin, who regularly played tennis with Lynette alongside a group of friends in Bayview, said she last saw Ms Dawson during a social game in the week leading up to Christmas 1981.

Ms McLoughlin said on that occasion, Ms Dawson appeared "quite distressed" and was begging her to come to her house for coffee.

She also told the court that Ms Dawson had a large grapefruit-sized bruise on her thigh.

Under cross-examination from Ms David, she admitted Ms Dawson did not say how she came to be bruised.

A then-teenager, who can only be known as BM, babysat for the Dawsons – prior to JC becoming their babysitter.

BM told the court that she witnessed Mr Dawson grab Ms Dawson by the arm and swing her "like a rag doll" into a door frame.

But Ms David has argued that BM had over the years changed her testimony and only used the term "rag doll" when she gave evidence to Mr Dawson's trial.

The couple's neighbour at the time Julie Andrew said she witnessed Ms Dawson "wailing" during a heated argument with Chris in her backyard.

Ms Andrew told the court that Lynette was "backed up" against a trampoline and Mr Dawson was "towering over her" and "roaring at her".

But Ms David argued that Ms Andrew had been influenced by journalist Hedley Thomas, who created the Teacher's Pet Podcast and that she had embellished her evidence.

The Warners Bay Hotel and the 'Sightings'

The bedrock of the defence case has been five claimed sightings of Ms Dawson after she went missing.

Mr Dawson has claimed that Ms Dawson phoned him several times after she was last seen before finally calling to say she would not be returning.

The only witness called by the defence was Paul Cooper, a 60-year-old Gold Coast man who had no connection to Mr Dawson or his family.

An email sent to Chris Dawson's lawyers by witness Paul Cooper. Photo / Supplied

He told the court that he had a chance meeting with Lynette Dawson at a pub at Warners Bay, in the Lake Macquarie region, in early 1982.

Mr Cooper said that Lynette had told him that she had two children but was running away from her family because of problems with her husband.

"She was waiting to get a passport from somebody who was going to meet her in a couple of weeks … She was going to go to Bali and then head off to another country overseas," Mr Cooper said.

He said he tried to convince her not to leave her children and told her that by disappearing without a trace people would believe she had been murdered by husband.

But Mr Cooper said he formed a view that it was the woman's intention to set "her husband up".

He saw an image of Lynette Dawson on A Current Affair in 2018, prompting him to contact Mr Dawson's solicitor Greg Walsh.

He said that he was "200 per cent" certain that the woman he spoke to in the hotel was Ms Dawson.

However the crown prosecution alleged that his memory was unreliable due to his history of drug use including marijuana and heroin.

The Dawsons' former Bayview neighbours, Peter and Jill Breese, both said they saw Ms Dawson working as a nurse at the Rock Castle Private Hospital – now South Pacific Private Hospital – at Curl Curl in June 1984.

Ray Butlin, a Dawson family friend, says that his wife Sue – before her death – told him of seeing Lynette at a Central Coast roadside fruit barn.

Mr Dawson's brother-in-law Ross Hutcheon said he had seen Lynette Dawson about three to six months after she had disappeared standing at a bus stop on Victoria Rd at Gladesville.

JC was the prosecution's star witness during the trial. Photo / NCA NewsWire

Elva McBay, a family friend, said she saw a woman who looked like Lynette Dawson run across the road at a parade for Prince Charles and Princess Diana in the Sydney CBD on March 28, 1983.

Crown prosecutor Craig Everson contended all of the claimed sightings were cases of mistaken identity or too fleeting to be considered reliable.

The Babysitter

In April 1983, Mr Dawson sought an order for the dissolution of his marriage with Lynette on the basis of abandonment.

He was awarded all marital assets including their home at 2 Gilwinga Drive, Bayview.

In January 1984, Mr Dawson married JC and later that year they moved to Queensland.

JC has told the court that she was "groomed" by Mr Dawson while she was still a student at the northern beaches school where he taught.

That categorisation has been disputed by the defence, who claimed that Mr Dawson "developed a care" for her, demonstrated by the fact they later married.

But she told the court that he left love letters and cards inside her school bag.

The court heard that in 1981, while she completed her HSC, she moved into the Dawson home as a live-in babysitter, during which time she would have sex with Mr Dawson while Ms Dawson was asleep.

Following Ms Dawson's disappearance, she moved in with Mr Dawson and his two children.

JC said she found a wardrobe full of Lynette's clothes and jewellery, slept in Ms Dawson's marital bed and was charged with looking after her two young daughters.

She moved to Queensland with Mr Dawson before they split in acrimonious circumstances in 1990, during which time she made several damaging allegations against him.

JC after she had moved into Mr Dawson's home following Lynette's disappearance. Photo / Supplied

The Hit Man

JC told the court of one occasion in 1981 – when she was still a schoolgirl – during which she alleged that Mr Dawson drove her to a building somewhere south of the Harbour Bridge.

She said that she was unfamiliar with the area and could not describe it.

She said she waited in the car, in her school uniform, while Mr Dawson went inside.

JC said that when Mr Dawson returned after 15-20 minutes, she asked him what they were doing.

"He said 'I went inside to get a hit man to kill Lyn but then I decided I couldn't do it because innocent people would be killed, could be hurt'," JC said.

The defence claimed that JC made the false allegation in the midst of a bitter separation and court proceedings in 1990.

As well, Ms David has argued that JC's account was unreliable because in a previous police statement, she said that Mr Dawson had made the "hit man" confession to her several weeks after they visited the building.

She told the court she had been mistaken about the timing and subsequently corrected her statement.

The move to Queensland

The crown has claimed that Mr Dawson had three motives to want to kill his wife; a deep animosity towards Lynette, he wanted "unfettered access" to JC and he wanted to avoid the financial consequences of a divorce.

Mr Everson has argued that Mr Dawson hatched four "plans" to leave Lynette and when they either failed or were abandoned, he turned to murder.

The last of those four alleged "plans" was Mr Dawson's attempted move to Queensland with JC just before Christmas in 1981.

In November, Lynette confronted JC, accusing her of taking "liberties" with her husband.

Then, just a few days before Christmas, Mr Dawson and JC piled their belongings and clothes into the back of his car and set out for Queensland with the intention of starting a new life.

The court has heard he left a note for Lynette saying: "Don't paint too dark a picture of me to the girls."

But they did not get to the border.

JC said she got sick, told him she missed her family and demanded he turn around.

They returned to Sydney, spending Christmas Day at his brother's home, while Lynette and her two daughters went to Chris' parents' house to celebrate.

Early in 1982, JC flew to the NSW Mid North Coast where she holidayed with friends and family at a South West Rocks caravan park.

She said that during her stay she received a phone call from Mr Dawson who told her: "Lyn's gone, she's not coming back."

JC said that Mr Dawson arrived in his Toyota Corolla station wagon at dawn, on or about January 10 or 11, and he drove her and her sister back to Sydney.

However there is dispute between the crown and defence about the timing – Mr Dawson claims he did not come to collect her until January 15, 16 or 17.

Ms David argued it went to several key points in the trial including JC's reliability and denials that he had "installed" JC in his home in a case "out with the old, in with the new".

During calls intercepted by the police in 2018, and played to the court, Mr Dawson lashed allegations against him as "bulls***" made up by his former wife amid their separation in 1990.

And in 1991, he told police that during his marriage to JC, he would "lay awake crying my heart out" hoping that Lynette would walk back into his life.

"The nights that I had spent extremely concerned about Lyn's whereabouts both for my sake, especially for my girls' sake and her mother's sake," Mr Dawson said.

"When you're living with somebody and you're trying to, sort of, work on a relationship with them, you obviously don't tell them that you're yearning for contact from your ex-partner."

Justice Harrison will deliver his judgment at a later date.

- Steve Zemek, news.com.au