Helen Milner bought an engagement ring with her new man just two months after her husband died, a court heard.
The death of Phil Nisbet, 47, on May 4, 2009 was originally ruled as suicide by police.
But a coroner raised doubts over his death, and a homicide investigation was launched two years later.
During that probe, an experienced police officer made enquiries at a Christchurch jeweller. Senior constable Hugh McLachlan discovered shop tax records showed Milner and new boyfriend Barry Hayton, who moved in to the family home within weeks of Mr Nisbet's death, had bought a $2299 engagement ring at Michael Hill Jewellers at the Palms Mall on July 12, 2009.
The revelation came on day four of Milner's High Court murder trial in Christchurch today.
It also emerged that Mr Nisbet's best mate was stunned to be told by Milner that he had committed suicide, saying it was ``completely out of character''.
Mr Nisbet, a club golfer, and model diecast car collector, was a friendly guy who loved his two sons, the court heard.
Milner phoned good friend Joseph Power on the day that she says she found Mr Nisbet dead in his bed.
"She said, 'I've got some bad news for you. Phil's died in his sleep','' Mr Power recounted.
She later told him Mr Nisbet had taken his own life.
"I just didn't believe it. It didn't sound like the guy I knew anyway,'' the self-employed gardener said.
"It just sounded completely out of character.''
Milner, 50, denies murdering her second husband by giving him a fatal overdose of the anti-histamine and sedative Phenergan, and possibly finishing him off with a pillow over his face. She also denies attempting to kill him twice on April 15 that year.
The Crown says she was unhappy in her marriage and was motivated to murder at the prospect of cashing in the $250,000 life insurance policy.
When Mr Nisbet first met Milner, they were "besotted'' with each other, Mr Power told the court.
He had spoken to Mr Nisbet regularly up to his death, but hadn't noticed him being stressed about anything in particular.
Mr Nisbet was a resilient character who had taken a few knocks, but "got up and looked life in the face and carried on''.
Today, the court also heard from a funeral director who met Milner the day her husband died.
Glen Rossiter-Campbell was surprised that she was acting "quite blase''.
"Normally you would get some tears when there's a suicide in the family. There's devastation. It's shock, it's grief.''
The trial, before Justice David Gendall, continues.