Chris Dawson found guilty of murdering wife Lyn in January 1982

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.

1800 RESPECT (1800 737 732)

Lifeline 13 11 14

Australian Associated Press