The sister of a Christchurch man who died in his bed says she began to suspect her brother's widow was involved in his death the month after the funeral.
Helen Milner, 50, is charged with the murder of her husband Philip Nesbit in May 2009.
The Crown says she fed him a lethal dose of the antihistamine Phenergan, which he was allergic to, and possibly smothered him.
It says Mrs Milner manufactured two suicide notes, with the one given to the family shortly after his death different from the one presented by police at the Coronial Inquest. She is also alleged to have sent herself a suicide text from her husband's phone.
Under cross-examination at the Christchurch High Court on Friday, Mr Nesbit's sister Lee-Anne Cartier said she had begun to suspect Helen Milner in June 2009.
Ms Cartier said she reached a point where she could no longer sympathise with Mrs Milner, but stayed friends with her in case she let something slip.
She said she began to contact friends and associates of Mrs Milner and Mr Nesbit to share her theories and began to forward all correspondence to police.
Proceedings were delayed by almost five hours on Friday morning because Mrs Milner needed treatment for her diabetes.