Lynette Dawson's former colleague tells court she saw bruises on her throat

A former colleague of Lynette Dawson has claimed she saw bruises on the nurse's throat days before the devoted mother disappeared 40 years ago.

Chris Dawson has pleaded not guilty to murdering his wife, who went missing from Sydney's Northern Beaches in January 1982.

Annette Leary said she would have "snatches" of conversation with Lynette during their shifts at the Warriewood Children's Centre.

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She told the NSW Supreme Court she once asked her colleague about bruises on her throat after Lynette and Chris had attended counselling together.

"She said that Chris had grabbed her throat and shook her a little and said 'if this doesn't work, I'm getting rid of you ... I am only doing it once'," Leary said.

Days later, Lynette's contract was terminated because she'd vanished.

The court also heard from centre director Barbara Cruise, who said Chris had called her to say "Lyn had gone away, she needed some time out and he didn't know when she was coming back".

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Cruise told the judge she had doubts about whether Lynette had disappeared of her own free will and once searched for Lyn's mother's name in the phone book, before calling her to raise her concerns.

The new claims came as Dawson's second wife, known only as JC, wrapped up her extraordinary evidence.

The court heard JC, who was the family's babysitter, married Dawson two years after his wife disappeared and her diamond ring was made from Lynette's engagement and eternity bands.

Central to the murder trial has been an allegation that Dawson once drove JC from the Northern Beaches and across the Harbour Bridge to a pub in Sydney's western suburbs.

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She claimed when he got back into the car he said: "I went inside to get a hitman to kill Lyn and then I decided I couldn't do it because innocent people could be hurt".

JC didn't tell anyone about that conversation until 1990, the same year she split from Dawson, and today rejected suggestions she made it up in the heat of divorce and a bitter custody battle.

During an explosive four days on the stand JC claimed she had been groomed, abused and controlled by Dawson since she was 16 years old.

She was challenged on every point and accused of being out for revenge.

When she was told her evidence was finally over she let out a huge sigh of relief.

The trial continues.