Malcolm Rewa's lawyer has accused Susan Burdett's son of murdering his mother to gain his inheritance.
Ms Burdett was raped and bludgeoned to death in her Papatoetoe home on 23 March 1992.
Rewa, 65, is on trial in the High Court at Auckland this month after pleading not guilty to murder. He has already been convicted of raping the 49-year-old accounts clerk but juries in two separate trials were unable to decide if he also murdered her.
Ms Burdett's son, Dallas McKay, took the stand today and told the the court about finding - and then losing - his biological mother.
Mr McKay was raised by his paternal grandparents after Ms Burdett gave birth to him when she was 16.
He told the court he grew up thinking his father was actually his brother and was 20 when he first met Ms Burdett, whom he called "Sue". They met at a South Auckland pub and discovered they shared a mutual love for tenpin bowling.
"It went very well, I was a bit nervous to start with, as you would [be], but we got on really well."
He told Crown prosecutor Gareth Kayes his relationship with Ms Burdett flourished in the few years they had together.
He commuted from Whangārei to Auckland for tenpin bowling events and kept in touch through phone calls and cards.
On the night the Crown alleges Ms Burdett was murdered, Mr McKay said he went out to play darts before returning to his Whangārei home around 11pm.
He called Ms Burdett, letting the phone ring twice to signal to her to call back so she could pay the phone bill, but she never called back.
Mr McKay said he went to work the next day, where he overheard a radio report that a 39-year-old woman who lived alone in her Papatoetoe home had been killed.
"I thought nah, nah can't be; wouldn't be; couldn't possibly be."
He called her workplace to find she had not turned up that day; a departure from her usually scrupulous work record.
He said he became increasingly concerned about her welfare and, when her death was confirmed, knew he was a police suspect from the beginning.
Today, Rewa's lawyer Paul Chambers put to Mr McKay that he was responsible for Ms Burdett's death.
"You had ample opportunity on the night and early morning the Crown says your mother died to travel from Whangārei, get into the house, kill your mother, leave the house and go back to Whangarei."
Mr McKay responded with a question: "And go to work?"
Mr Chambers said Mr McKay, who was 22 at the time of Ms Burdett's death, had everything to gain from killing her; including inheriting $250,000 through her life insurance policy.
But Mr McKay said he was not aware Ms Burdett had altered her will until after her death.
He told Mr Chambers he had got it "completely wrong". "I'm not the one on trial here," he said.
Other aspects of Mr McKay's evidence were suppressed.
The trial before Justice Venning and a jury is set down for four weeks.