Chris Dawson and Lynette Dawson were married with two children before she disappeared.

Chris Dawson has been found guilty of murdering his wife Lynette and disposing of her body more than 40 years ago.

Dawson pleaded not guilty to the murder of his wife, who disappeared from their Bayview home on Sydney's northern beaches in the summer of 1982 and fought the allegations during his 10-week trial earlier this year.

However Justice Ian Harrison on Tuesday found him guilty, after accepting the Crown prosecution's argument he killed his wife and disposed of her body so he could be with the family's teenage babysitter.

Dawson, 74, was found to have killed his wife in January 1982, just weeks after he had unsuccessfully attempted to run off with his former student to start a new life in Queensland.

The former teacher and rugby league player's defence had argued he had neither the opportunity nor the motive to kill the mother of his two children.

However, Justice Harrison accepted evidence from Lynette's family and workmates that he had been physically abusive and harboured a deep animosity towards his wife.

Lynette Dawson disappeared in January 1982 - her body has never been found and she never contacted her friends or family, including her two children.

The 33-year-old nurse was last seen on Friday, January 8, 1982 when she spoke to her mother Helena Simms on the phone.

The crown prosecution alleged she was killed either Friday evening or early the following morning.

Dawson told detectives during a police interview in 1991 that he had dropped off his wife at a Mona Vale bus stop and it had been planned she would meet him later that afternoon.

However she did not arrive at the Northbridge Baths, where Dawson worked as part-time lifeguard.

He had claimed Lynette phoned him at the baths to say she needed time away before ultimately telling him during another call that she would not be returning.

Central to the case was JC, one of Dawson's former students who became the couple's live-in babysitter in 1981.

JC told the court that during this time she would have sex with Dawson while Ms Dawson was asleep.

The Crown prosecution argued Dawson killed Lynette because he was "besotted" with JC and wanted "unfettered access" to her.

In late 1981, Dawson and JC packed his car full of their clothes and belongings and set out for Queensland to start a new life.

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

But JC forced Dawson to turn the car around before the border after she grew ill and told him that she missed her family.

In early 1982, she travelled to South West Rocks to holiday with her friends and family.

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

JC and Dawson went on to marry in January 1984 before separating in acrimonious circumstances a little over six years later.

In 1990, she made several damaging allegations against Dawson, including claims of domestic violence and that he had once contemplated hiring a hitman to kill Lynette.

JC told the court of one occasion in 1981 during which she alleged Dawson drove her to a building somewhere south of the Harbour Bridge.

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

Dawson's defence had relied on five claimed sightings of Ms Dawson in the two years following her disappearance.

The Dawsons' former Bayview neighbours, Peter and Jill Breese, both claimed they had independently seen Ms Dawson working a Curl Curl hospital in June 1984 - more than two years after she disappeared.

Ray Butlin, a Dawson family friend, said before her death, his wife Sue had told him of seeing Lynette at a Central Coast roadside fruit barn where she worked.

Dawson's brother-in-law Ross Hutcheon told the court he saw Lynette while driving along Victoria Road in Gladesville about three to six months after she disappeared.

Elva McBay said she attended a parade for Prince Charles and Princess Diana on March 28, 1983, when she saw a woman who looked like Lynette Dawson run dangerously in front of a motorcade.

The defence's star witness, Paul Cooper, said he had a chance meeting with Lynette Dawson at a pub at Warners Bay, in the Lake Macquarie region, in early 1982.

But Justice Harrison accepted Crown prosecutor Craig Everson's argument that all these sightings were either unreliable or cases of mistaken identity.