A Queensland woman was threatened at knifepoint over money owed by her husband before he was shot execution-style in his office, a Brisbane court has heard.
Gion Tansley was married to Philip Carlyle when he was shot four times in the head at a Gold Coast business complex in April 1997.
Mr Carlyle's former business associate Neil Andrew Pentland, now 72, denies carrying out the killing.
Mrs Tansley said a man came to a property where she was house-sitting while Mr Carlyle was overseas.
While holding a knife the man said Mr Carlyle should pay back money he owed.
Mrs Tansley told the court she was not aware of any debt.
But she was aware of numerous businesses - like a palm tree nursery, a Mexican restaurant and a factory manufacturing corn flour for tortillas - in which Mr Carlyle had been involved over some time.
Many of these had failed.
Crown prosecutor David Meredith says Pentland and Mr Carlyle had an internet service provider business and were starting an online insurance-related service.
Mr Meredith told the court the pair argued over the value of an overseas work trip Mr Carlyle was due to take days after his death.
While in the US Mr Carlyle was due to a meet a woman he had been having an online affair with, but had never met.
The court also heard Pentland and Mr Carlyle had a life insurance policy that would pay out $500,000 if either man died.
But Pentland's barrister Saul Holt told the court his client claims the business - not an individual - stood to get the money.
Mr Holt said the prosecution's case relied on weak and irrational evidence and motive.
"Circumstantial cases can be powerful, but this one is not," Mr Holt said.
Police charged Pentland with Mr Carlyle's murder in June 2017 after detectives reignited their investigation into the murder.
Mr Carlyle's body was found by a security guard at the pair's Robina business premises on the evening of April 13 after his wife raised the alarm.
He had been at the property to tidy up some loose ends before departing on the planned overseas trip.
Pentland pleaded not guilty to murder at a judge-only trial in the Brisbane Supreme Court on Monday.