After recording his wife venting for hours, Richard Dudley Kelsey got a rifle from his bedroom safe and shot her, later saying he wanted to get rid of her, having had "a gutful".
"She goes on and f***ing on and on and on, and I said f*** it - boom - just shot her," Kelsey told police, a court has been told.
Kelsey has denied murdering his 67-year-old wife Gail at their home at Chambers Flat, south of Brisbane, in November 2019.
The 76-year-old offered to plead guilty to manslaughter over Mrs Kelsey's death at the start of a Brisbane Supreme Court trial, but the plea was not accepted by prosecutors.
Kelsey's actions and some words were not in accordance with his statement to officers that he wanted to frighten his wife, crown prosecutor David Nardone told jurors in his closing on Thursday.
Kelsey was mostly silent while recording his wife talking for more than two hours so he could show how she was acting, the court heard.
The recording stopped before Kelsey walked 19 metres to the gun safe in his bedroom where he chose his most powerful rifle, rather than a loaded gun, Mr Nardone said.
Camera footage shows Kelsey pointing the rifle at his wife at close range and shooting her in the abdomen before loading a second bullet in the chamber.
"The need to shoot her again fell away, just as Mrs Gail Kelsey fell off the chair and slumped to the ground," Mr Nardone said.
Kelsey appeared uncaring, ringing emergency services to say what he had done before accessing a banking website, he added.
The court heard the couple's relationship had deteriorated, with Kelsey saying they should have divorced 15 years earlier.
Jurors are required to consider the defence of provocation, but Mr Nardone said while Mrs Kelsey was talking in frustration about her husband's family, she was only venting.
In "very telling" words , Mr Nardone said, Kelsey told officers: "I had a gutful, just wanted to get rid of her, the divorce and everything."
Kelsey admits killing his wife but there was no murder confession and prosecutors were relying on circumstantial evidence, defence barrister Tony Kimmins said.
It is an absolute godsend Kelsey taped the conversation, in which he spoke for the first time after one hour and 53 minutes of his wife venting, Mr Kimmins said in his closing.
The recording, played during the trial, "wasn't very pretty at all", with Mrs Kelsey berating her husband while wanting him to have nothing to do with his family.
While the trial had been told Mrs Kelsey hardly swore, Mr Kimmins tallied the times she used specific swear words in the recording, with some of her supporters leaving the court crying as he did so.
Mr Kimmins argued Kelsey was provoked, having told officers his wife did not show her "toxic side" to others.
Kelsey told police things had become too much, that he did not aim the gun and "it just went off with a loud bang".
Asked what he intended when he fired the gun, Kelsey replied: "Buggered if I know, to tell you the truth, mate," Mr Kimmins said.
Justice Lincoln Crowley is set to address jurors before they retire to deliberate.
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