Ewen Macdonald's wife has told a jury that when she asked if he had killed her brother, Scott Guy, he emphatically denied it.
Mr Macdonald is on trial in the High Court at Wellington charged with murdering his brother-in-law in July 2010, at his rural Feilding property.
Anna Macdonald told the court on Thursday she had visited her husband many times in prison after he had been charged with her brother's murder.
The defence lawyer, Greg King, asked her if she had ever asked Ewen Macdonald if he was guilty.
She says he said to her, I swear I didn't do it.
Mrs Macdonald also told the court that after her husband had damaged Scott and Kylee Guy's house, he felt terrible.
She says in the months after the vandalism, he tried hard to make up for his actions, and he seemed to put any ill-feelings about Mr Guy behind him.
Earlier postal workers told the court about notes they found in Scott Guy's letterbox before the Feilding farmer died that read "you cheating whore" and "now you know what it feels like to lose something you love".
Rural delivery worker Brett MacDonald told the court on Thursday that he found a note in Scott and Kylee Guy's letterbox about two weeks after a house owned by the couple burned down.
He said the note read: "you cheating whore - what goes around comes around."
His colleague Emma Beaney said she found one note after the fire and another after a vandalism attack on the couple's home.
She said one of the notes said "stay away from him Kylee you whore" and the other "now you know how it feels to lose something you love".
In cross-examination, Ms Beaney denied that she had made up her story and said there had definitely been notes left in the Guys' letterbox.