A "Dear John" letter was probably written by the wife of an ambulance officer now accused of murdering her 40 years ago, a jury has been told.
Roxlyn Bowie also probably penned one to her parents saying she had left her husband and the kids, according to a forensic document examiner.
Linda Morrell gave evidence on Thursday at the NSW Supreme Court trial of John Douglas Bowie.
The 72-year-old has pleaded not guilty to murdering Roxlyn Bowie, who was 31 when she vanished from their Walgett home in northern NSW on June 5 1982.
The Crown alleges he killed his wife so he could have an unfettered relationship with another woman and may have disposed of her body by feeding her to pigs.
A neighbour has told the jury of noticing the "Dear John" letter under a sugar bowl in the Bowies' house when she helped him search for his wife on the night she disappeared.
The letter includes: "I'm leaving you with the kids for good" and "I've thought about it for a long time now and tonight finally did it".
The jury also has been told of a letter to her parents, which arrived at their Sydney home on June 8.
It includes: "Just a short note to say that I have left John and the kids for good" and "Please don't be hard on John because it wasn't his fault that I left".
The Crown has suggested the letters were written under duress, but the defence says if real, jurors might think she left of her own accord.
Ms Morrell said she compared the handwriting on the two letters and one envelope with that on 15 items known to be written by Ms Bowie.
She also had five letters written by Bowie.
Ms Morrell found a number of similarities between the items known to be written by Ms Bowie and the three questioned documents.,
"It is my opinion that Roxlyn Bowie has probably written both letters and the envelope," she said.
She said five of her known letters started with the words "Just a short note", as did the letter to her parents.
But the latter differed in having a small gap between the j and the u, as did some of Bowie's handwriting for the word "just".
Ms Morrell said the "his" included in "because it wasn't his fault" letter to the parents had been overwritten and the original word was "her".
A statement given by Bowie to police on August 19, 1982 was read to the jury.
"Although our marriage was not a great one, things went along reasonably smooth most of the time," he said.
Between 6.30 and 7pm on June 5, he told his wife he was going down to the Imperial pub for a few beers.
"She said if I do 'I won't be home when you get back'."
He left to drink at the pub and went onto the Walgett RSL Club before returning home.
"I noticed the TV was on, the lounge room light was on and the kitchen light."
He said both children were asleep in their room, while the back door was open and his wife was missing.
He visited various people trying to find her, while a neighbour helped him search the Bowie home and handed him a piece of paper.
"I read the note which was from Roxlyn in her handwriting and I broke up not believing she would leave me."
The next morning he noticed a blue leather suitcase was missing, as well as a few of his wife's dresses, jeans and jumpers and about $100 cash they kept in the dressing table.
The trial continues before Justice Dina Yehia.
