But that recollection clashes with what other witnesses have told the court.
Mr Guy's sister Nikki said last week that it was Macdonald who suggested on the day of the killing - July 8, 2010 - that he had been shot and not had his throat cut.
The first person to find him, neighbour David Berry, told her the throat wound looked as if it was caused by a knife.
Nikki Guy said Macdonald twice corrected Mr Berry, saying, "No, he was shot." And farm worker BJ Worthington also said that Macdonald had said "someone shot him" on the day of his death.
Macdonald told detectives he only got as close as about six or seven metres from the body.
Police discovered Mr Guy was shot when they found bullet fragments in his throat and until that was confirmed it was something only the killer would have known.
The Crown alleges Macdonald - motivated by jealously and fears that his future on the farm was in jeopardy - killed Mr Guy, his brother-in-law, in his driveway.
Macdonald denies being the one who pulled the trigger and is defending the charge.
Macdonald told Detective Graeme Parsons how he was phoned by a neighbour and told there had been an accident and Mr Guy was dead.
He rushed there on a quad bike and saw Mr Guy's ute parked on the driveway and his body close by.
"I could not say much more about Scott as I did not want to look any more, and it was very obvious that he was dead, he looked limp and flat."
Macdonald also told Mr Parsons that he noticed the farm gates were locked. It was unusual because Mr Guy shut the gates only if he was moving stock, he said.
The Crown says the gates were locked by the killer to trap Mr Guy, who had to get out of his ute in the pre-dawn dark before the killer stepped out of the shadows - and started shooting.
Macdonald also told police he wondered if he was supposed to be the target and spoke to his father, Kerry, about it.
"I rang my father and he said he didn't think so."
He speculated that Bryan Guy had been involved in a legal stoush with a milk supplier and wondered if the killing was connected to that.
He also suggested a former boyfriend of Nikki Guy could be responsible because Macdonald and his wife Anna, Mr Guy's sister, had told him he was not welcome in their home. They heard that the former boyfriend believed Macdonald and Anna were trying to break him and Nikki up.
Shortly before he died, Mr Guy and Macdonald went to a farming conference in Invercargill. Macdonald said they both came back "on a high" and were happy and confident about the future.
It was the first time he had been away with Mr Guy for a long time and it had gone well.
"We had a number of talks about the farm and what we wanted to achieve.
"We were on the same page about working smarter and not harder."
The jury will next week watch a DVD of another police interview with Macdonald, this time after he had been charged with murder.
