"I have nothing to do with that," Macdonald said.
"It looks obvious, these leading-up-to events, but I'm not that psycho."
The Crown alleges Macdonald carried out the vandalism and arson to intimidate Mr Guy and his wife Kylee off the farm.
The more than four hour-long police interview, shown to the jury yesterday and today, was conducted at the Palmerston North police station last April 7.
Minutes before the interview ended, Macdonald told Detective Laurie Howell: "I guess I won't be going home tonight, will I?"
Mr Howell replied he doubted it.
Macdonald was arrested and charged with murder later that afternoon.
Earlier in the interview, Macdonald said he could "see the finger points at me" but maintained he did not do it.
Mr Howell said he did not have an alibi, knew the area well and had the motive of control of the farm.
Macdonald replied: "Personally I don't think that would have achieved anything for me."
He said his work hours had increased and it had been a "total pain in the ass" without Mr Guy on the farm.
Detective Glen Jackson said there was plenty of opportunity for Macdonald to kill Mr Guy before the morning milking.
Macdonald replied another farm worker rostered on that morning would have suspected something.
Mr Jackson put it to him that it was "not normal" to burn down somebody's house, to which he replied he would not take a life.
Macdonald told police he committed the arson because he "thought that it would be funny".
"It wasn't directed at Scott and Kylee in vengeance."
Asked why he later damaged the new house on the property, Macdonald said the partnership on the farm was not fair and he had "slogged my guts out".
He denied any knowledge of notes left in the Guys' letterbox.
The trial today also heard evidence on the scene examination of the driveway where Mr Guy was gunned down.
Mr Jackson said officers scoured the side of Aorangi Rd, metres away from where he was found dead.
He found distinctive prints on the driveway near the body and on a grass verge, which were plotted by members of the serious crash unit.
Some were found close to the fence line, which surprised Mr Jackson.
"It's not an area you would normally associate with anyone walking through."
The Crown alleges Macdonald used a bicycle to ride to Mr Guy's house before cycling back to do the morning milking within a 17-minute window.
In his cross-examination, defence lawyer Greg King put it to Mr Jackson that no evidence of a bike was found, despite a thorough scene examination.
Mr Jackson replied he did not find anything at the scene to support a bike being involved.
Detective Ross Peat gave evidence that he noticed a "wavy pattern" in a couple of places near a cow shed where Mr Guy's chocolate labrador and puppies were kept.
The Crown alleges Macdonald stole and killed three of the puppies to throw investigators off the trail.
Police searched in a grid through a paddock and found a set of tracks leading from the road to the shed.
The track impressions were flagged, numbered and cast - but the two impressions at the cow shed were only photographed.
The prosecution case is that Macdonald wore dive boots with a distinctive pattern, but later disposed of them.
Mr Peat said he also found smudge marks on the driveway gate.
From the impressions he concluded a glove rather than a cloth had been used to touch the gate.
The Crown alleges Macdonald shut the gates at the end of Mr Guy's driveway to trap him as he left to do the morning milking.
He was then gunned down in near-darkness, illuminated only by the lights of his ute, when he stepped out of the vehicle to open the gate.
The trial before Justice Simon France and a jury of 11 continues tomorrow with evidence from Kylee Guy on the labrador puppies.
- Additional reporting: Andrew Koubaridis of the New Zealand Herald