John Douglas Bowie jailed for killing wife Roxlyn Bowie more than 40 years ago in Walgett

But on Friday, her now 72-year-old husband John Douglas Bowie was told he would likely spend the rest of his life behind bars for killing the 31-year-old after manipulating her into writing the callous message.

Bowie was sentenced to a maximum of 24 years in prison with the possibility of parole in 2037.

In October, a jury found Bowie guilty of murdering his then 31-year-old wife in Walgett on or around June 5, 1982.

Bowie has always denied his involvement in the disappearance, but Justice Dina Yehia was satisfied he killed his wife in order to seek a sexual relationship with a younger woman.

"He is now 72 and he will not be eligible for release for some time," she told the NSW Supreme Court on Friday.

"He may die in custody."

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As Justice Yehia handed down the sentence, Bowie sat in the courtroom, red-faced and with a hand over his mouth.

Meanwhile, Bowie's sister Christine Maddocks and daughter Brenda Boyd burst into tears.

"I'd prefer to have 24 years of Roxlyn than 24 years of John being locked up," Ms Maddocks told AAP.

"This kind of thing just consumes your whole life and it's no closure for Brenda."

Ms Boyd has spent most her life looking for her mother after the devoted carer disappeared when her daughter was six, leaving behind only a letter.

The "Dear John" letter, which was in Mrs Bowie's handwriting, said she was leaving her husband and her kids and told them expressly not to contact her.

In a subsequent letter addressed to her parents, she stated: "Please don't be hard on John, it wasn't his fault".

Her body has never been found.

Justice Yehia was satisfied Bowie coerced his victim to write those letters before he killed her so he could "lay the claim that she simply abandoned him and the children" and move closer to his mistress in Sydney.

Prior to her death, Mrs Bowie was a loving mother who was doing the best she could in a relationship with a man who was a self-admitted womaniser and heavy drinker.

Justice Yehia said this meant it was unlikely she had abandoned her children just because she'd had enough of her relationship with her husband.

She could not determine exactly when Bowie manipulated his wife into writing the letters or whether she had been murdered in their Walgett home, but the judge was satisfied he planned the killing and disposed of her body.

The court heard Bowie had grown up in an unstable household, often witnessing physical violence between his mother and father, and had a history of violent acts against women.

He spent most of his life plagued by alcohol dependency and suffered from several mental and physical ailments.

Bowie was arrested for his wife's murder in 2019 and will not be eligible for parole until October 2037.

Australian Associated Press