Chris Dawson found guilty of murdering his wife Lynette

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 at the NSW Supreme Court on Tuesday, Justice Ian Harrison found Dawson guilty of murder, concluding a 40-year-old mystery.

Justice Harrison said that while the evidence against Dawson was "wholly circumstantial", it was "persuasive and compelling".

"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, with the intention of causing her death," the judge said.

He added that there was no reasonable explanation for the mum's disappearance from the Northern Beaches of Sydney at age 33.

"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 said.

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

Dawson claimed he had spoken to his missing wife over the phone a number of times after she vanished, with her telling him she "needed some time away".

The judge dismissed these claims as untruthful saying the accounts of the supposed phone calls were "lacking in context and pregnant with clichés".

Dawson resolved to kill wife after starting affair

Justice Harrison said he believes Dawson's "obsessive infatuation" with his teenage girlfriend — identified as JC — led to the former rugby league star's decision to kill his wife.

Soon before Lynette's death, JC and Dawson had travelled to Queensland to start a new life, with the latter missing Christmas with his family.

But after returning home, JC went on a trip with friends and was beyond Dawson’s "physical reach and out of his control".

"Mr Dawson was in Sydney hundreds of kilometres from JC with no knowledge of what she was doing or with whom, while he remained shackled with a wife he had only days before shown himself to be more than enthusiastic to leave," Justice Harrison said.

"I'm satisfied that the prospect that he would lose [JC] so distressed, frustrated and ultimately overwhelmed him that tortured by her absence up north, Mr Dawson resolved to kill his wife."

Evidence by JC that Dawson had driven up to South West 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.

According to evidence given at trial, JC moved into the Dawson home within days of Lynette's disappearance. The pair married in 1984 and separated in 1990.

Dawson taken into police custody

The former local rugby league star sat next to his older brother Peter as the judge read out the verdict in front of a packed court room. He was taken into police custody after it was announced.

A live stream of the judgement on YouTube attracted more than 20,000 concurrent viewers on Tuesday afternoon.

The verdict comes after the judge spent seven weeks considering witness testimony and submissions in Dawson's two-month long murder trial.

The crime was brought back into the public spotlight in recent years following a popular podcast titled 'The Teacher's Pet' by The Australian newspaper – something the justice said was a "significant factor" in the case before the court.

"I have taken into account how the podcast may have corrupted evidence given in this court," Justice Harrison said.

Dawson's lawyer, Greg Walsh, told reporters outside the court it is "probable" his client, who is suffering from dementia, will appeal the conviction.

Lynette's family call on Dawson to reveal body location

Following the judge's decision, Lynette's brother, Greg Simms, thanked people for their support and urged Dawson to tell the family where her body is located.

"The journey is not complete," he told the ABC.

"She's still missing. We still need to bring her home. We would ask Chris also to find it in himself, to be allow us to bring him home for peaceful rest.

"Finally showing some dignity, she deserves."

with AAP

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