Months before Philip Carlyle was shot dead, his business associate's wife accessed his emails finding evidence of an internet affair.
Dianne Pentland says something about her husband's marketing manager raised her concerns.
Her husband Neil Andrew Pentland, 72, is now on trial charged with killing Mr Carlyle in their Gold Coast business complex in April 1997.
Mrs Pentland told the Brisbane Supreme Court on Tuesday she asked her son to set up the access to Mr Carlyle's emails in late February or early March.
She told her husband about the flirtatious email exchanges.
"His reply was, 'I don't wish to know about it. He's a fool'," Mrs Pentland said.
The court was also told Mr Carlyle was a business deal-breaker who brought important sales skills to Pentland's business.
Adam Pentland told the court his father whimpered and became agitated when told Mr Carlyle was dead.
"He didn't take it very well," he said.
It was Adam Pentland and a security guard who found Mr Carlyle's body in an air-conditioning plant room at the Robina business premises on the evening of April 13.
Adam Pentland said the hackles on the back of his neck went up when he saw a large amount of blood on the floor after taking two steps into the room.
The security guard went inside, finding Mr Carlyle's body.
The court has heard Mr Carlyle had a string of enemies due to debts and failed business deals.
Accountant John Fraser said Mr Carlyle came into his office "in a very flustered state (and) a little bit edgy" after two men visited his house.
"He said two heavies were at his front door .. demanding money," Mr Fraser said.
"He said he'd slammed the front door and ran through the house, got in his car and drove down to me."
The court also heard a string of people might have had a grudge with Mr Carlyle.
Business consultant Guy Bagot told police during their investigation there were 10 or 12 people who might have felt animosity towards Mr Carlyle.
Mr Carlyle was involved in numerous business ventures including a palm tree nursery, a bakery, a Mexican restaurant and a factory manufacturing corn flour for tortillas.
But many of these failed.
Pentland and Mr Carlyle had an internet service provider business and were starting an online insurance-related service.
Crown prosecutor David Meredith has told the court the pair argued over the value of an overseas work trip Mr Carlyle was due to take days after his death.
During the trip, Mr Carlyle planned to meet the woman he had been having an online affair with but had never met.
Pentland's barrister Saul Holt earlier told the court the prosecution's case relied on weak and irrational evidence and motive.
"Circumstantial cases can be powerful, but this one is not," he said.
The trial continues.