The teacher, the wife, the babysitter and the 40-year wait - what happened to Lynette Dawson?

At first glance, this simple message printed in a 1982 newspaper appears to be nothing more than an emotional plea from an abandoned husband.

"Lyn, I love you, we all miss you. Please ring. We want you home, Chris," the ad read in the classified section of The Daily Telegraph on March 27, 1982.

At the time, the short note probably seemed innocuous, stuck between an ad from a lonely widow and a 19-year-old girl looking for a boyfriend.

It may have even invoked feelings of pity or heartache from readers.

But, according to Tuesday's New South Wales Supreme Court ruling, the writer, Chris Dawson, had already killed Lynette – the woman he was begging to return home – more than two months earlier.

When delivering his verdict this week, Justice Ian Harrison said he was satisfied beyond reasonable doubt that Lynette was dead and she died on, or around, January 8, 1982.

Dawson was found guilty of her murder, with Harrison finding he had "resolved to kill his wife" after becoming "infatuated" with his student and teen babysitter, known as JC, whom he later married.

He said it was clear the mother-of-two had not voluntarily left her home, as had been suggested by Dawson throughout the trial.

The 33-year-old nurse was last seen on Friday January 8, 1982, when she spoke to her mother on the phone. She was never seen or heard from again, and her body was never found.

Dawson's advertisement in the newspaper was published the day after his wedding anniversary, with prosecutors using it as proof he knew his wife was dead.

During the trial, the court heard the advertisement pointed to a hole in the 74-year-old's story, as the teenage babysitter he was engaged in a sexual relationship with had already moved back into the Sydney northern beaches home he once shared with Lyn.

"The day The Daily Telegraph published that, (JC) was living as the accused's de facto partner, she was sleeping in the marital bed, she was wearing Lynette's clothing in Lynette's home," prosecutor Craig Everson told the court.

"If Lynette Dawson had been alive and seen the advertisement and returned home as requested, what would she have found? She would have found (JC) as having taken her place as the spouse to her husband and the mother to her children."

Before Lyn vanished, JC had moved in with the married couple as a live-in babysitter.

However, the teen was forced to move out after Lyn accused her of "taking liberties" with her husband.

In early 1982, the teenager went to South West Rocks on NSW's Mid North Coast on a holiday with her family and friends, during which she phoned Dawson every day.

JC said during one phone call Dawson told her: "Lyn's gone, she's not coming back, come back to Sydney to help me look after the children."

This is when she moved back into the Bayview home and began sleeping in Dawson's bed and wearing his wife's clothes.