Former ambulance officer John Douglas Bowie has been found guilty of murdering his wife Roxlyn in rural NSW 40 years ago.

A NSW Supreme Court jury took less than four hours to reach its verdict on Monday afternoon after a lengthy murder trial.

Bowie has always denied involved in the disappearance of his then 31-one-year old wife from their home in the northern NSW town of Walgett on or around June 5, 1982.

Mrs Bowie’s body has never been found and she has not contacted anyone or been seen since.

Succeeding in their circumstantial case, prosecutors alleged Bowie forced Roxlyn to pen two letters saying she had left her husband and children, and then killed her afterwards. 

The jury heard she was a loving mother and that it was implausible she had simply left her family.

The Crown claimed his motivation for the murder was a desire to have an unfettered relationship with another woman living in Sydney. 

Evidence was also shown to the jury suggesting Bowie had a tendency of violence towards his domestic partners.

One witness who gave evidence at trial claimed they saw someone with Bowie’s description burying a bra and pantyhose in a gully at a golf course in Walgett.

Excavations of a property near the Bowie family home also uncovered a dress ring which the Crown claims was owned by Roxlyn.

Prosecutors alleged Bowie made a number of admissions to the murder, including telling one woman he had “killed someone before” and separately saying pigs left no trace of a body.

Bowie’s counsel Winston Terracini SC rejected the prosecution case, saying there was no forensic evidence of a murder or even a struggle occurring at the couple’s Walgett home.

The jury heard because Bowie was a violent man who drank heavily and womanised, his wife had ample reason to leave him voluntarily.

Mr Terracini said there were flaws in the police investigation and argued that the lengthy delay in bringing the criminal proceedings has caused some disadvantage.