In 1982, Roxlyn Bowie vanished. 37 years later, her husband has been charged with her murder.

This article was first published on October 16 2018, and was updated on October 6 2019 following the arrest of John Bowie.

— With AAP.

Almost four decades after his wife Roxlyn disappeared, John Bowie will face a Sydney court charged with her murder.

The 69-year-old – due to appear at Parramatta Bail Court on Sunday – denies killing Roxlyn, who vanished from home in the far north NSW town of Walgett on June 5, 1982.

Her body has never been found.

“I don’t even know if she’s dead or not,” Bowie told reporters on Saturday as detectives escorted him through Sydney Airport en route to Surry Hills Police Station.

Bowie was charged with murder on Saturday at Surry Hills, having been arrested at Queensland’s Woodford Correctional Centre on Friday.

A coroner in 2014 found she was dead but couldn’t determine the cause of death.

Police admit their circumstantial case will be challenging to prove without Ms Bowie’s body.

“It’s happened before, we know the road ahead will be challenging,” Detective Superintendent Danny Doherty told reporters on Saturday.

“We’ll have our day in court and hopefully get some justice for Roxlyn and her family.”

He wouldn’t reveal what police allege was the motive for murder.

“That… will come out and play out in court,” the detective said.

New interviews with witnesses and technical advances in uncovering forensic evidence helped progress the case.

Two separate searches in Walgett in the past year revealed personal items, including a silver ring with the letter “R” and black and gold packaging for a Swann-Morton surgical blade.

A $1 million for information leading to the discovery of Ms Bowie’s body remains in place.

What we know about the disappearance of Roxlyn Bowie

Brenda Boyd remembers her mother kissing her goodnight for the very last time.

That was 37 years ago on the night of Saturday, June 5 1982. Her mother Roxlyn Bowie, 31, then vanished from the family’s home in the New South Wales town of Walgett, leaving behind her husband John Bowie, six-year-old Brenda and her son Warren, who was just a week away from his second birthday. She hasn’t been seen since.

Mrs Bowie was described as being of Caucasian appearance, 167cm tall, of a slim build, with brown hair and hazel eyes. She regularly wore reading glasses.

The case is full of mystery – it is still unknown what happened to Roxlyn all those years ago. Speaking to A Current Affair, Brenda said nearly four decades on, she still needs closure.

Following Roxlyn's disappearance, Ambulance driver John told police the couple had argued and Roxlyn had warned him that if he went to the pub, she'd leave him. He'd gone anyway and when he returned she had vanished.

He reported his wife missing the next day but police told him not to worry and that she'd be home in a few days.

John rang Noelene Knight, one of Roxlyn's closest friends who lived in Sydney, to tell her the news. When he told her Roxlyn had left the children behind, Noelene knew something wasn't right.

Roxlyn "idolised" her children and was a caring mum who would never leave him, Noelene said. Others who knew Roxlyn, including friends, neighbours and babysitters also described her as a dedicated, loving mother.

A friend discovered a note under a sugar bowl in the Bowie's dining room. Nine News reported it read:

"Dear John, I’m leaving you with the kids for good. I’ve thought about it for a long time now and tonight finally did it. I’ve packed a few things and you can have the rest. I don’t want anything to remind me of you or the kids. Don’t try to find me, because I will never come back to you. Bye, Roxlyn."

Three days after her disappearance, Roxlyn's parents received a letter sent from Coonamble, about 100kms from Walgett.

Seemingly signed by their daughter, the letter said she was making her way to South Australia or Western Australia to start a new life.

These letters have continuously baffled investigators. Both were written on the same notepad, on consecutive pages and three handwriting experts have concluded that they were written by Roxlyn.

Brenda does not believe her mother wrote them.

Six days after his wife's disappearance, John applied for a transfer to Sydney. It was here that he remarried the following year and pawned off his ex-wife's jewellery.

In 2018, John told A Current Affair he did not kill Roxlyn.

"I've got no idea where she's at or what has happened to her," he said. "I swear on the bible, I did not have anything to do with the disappearance of Roxlyn."

Despite his denial, his daughter Brenda believes her father knows more than he's letting on.

"I think there's things that my dad might know that he hasn't told me," she said.

"I think I deserve the truth, I deserve answers, my children deserve answers."

Deepening the mystery, the inquest was told Roxlyn’s DNA was not found on the stamp or envelope on the letter sent to her parents.

Detective Chief Inspector Russell Oxford shared three theories with the inquest:

1. Roxlyn wrote the notes with the intension to leave but they were later used by someone else as a cover for her disappearance

2. She was forced to write the letters

3. She wrote the letters and left.

The inquest found Roxlyn had died on or about the night she died but the cause of death was undetermined. Her body has not been located.

Russell Oxford has continued to work on the case in the years since.

"I’ve been working on this case for thirty years and I don’t want it to go away, I want to find out myself. I suppose in a way, the driving force behind this is Brenda’s quest for answers," Russell said.

An investigation was led by the State Crime Command's Robbery and Serious Crime Squad, called Strike Force Maluka, which resulted in the arrest of John Bowie nearly 40 years after the alleged crime.