The Crown alleges Mr Guy's brother-in-law Ewen Macdonald burned down the house and later vandalised a new house being built on the property to intimidate Scott and Kylee Guy off the farm.
Macdonald, 32, has denied shooting and killing Mr Guy, 31, in his driveway in the early morning darkness of July 8, 2010 after mounting tensions over the Feilding family farm they co-managed.
In a written statement read to the jury in the High Court at Wellington today, Kylee Guy said she and Scott had originally wanted to do up an old house on their property but it involved too much work.
They sold it to a removal company for $8000 and received a $2000 deposit, with the rest to be paid once the house was shifted off the property.
But the house was burned down in an arson attack in October 2008, which Macdonald later admitted to.
Mrs Guy said she was "devastated" when Scott told her the old house was destroyed.
The Guys later built a new house on the property.
Mr Guy's father Bryan Guy read out a statement to the jury in which he said the house was completely destroyed by the fire.
He said the arson had disrupted the construction of the new house.
"I don't think Scott and Kylee had any emotional attachment to the old house, so I don't think they saw it as any huge loss. That's my impression."
Detective Felicity Mansell said firefighters arrived about midnight on the night of the fire.
She and fire investigators tried to find where the fire started but the extensive damage hindered that.
"There was very little in the way of evidence to show us where the point of origin was."
Mrs Mansell spoke to neighbours in her investigation including Macdonald's wife, Mr Guy's sister Anna Macdonald.
Macdonald came into the kitchen while they spoke but she did not talk to him.
Investigators turned up no leads so police put out a media release seeking information.
Mrs Mansell said nothing in her area canvas to suggest wayward children or criminals in the area were responsible.
She said there was nothing that led her to believe it had been an insurance scam.
The jury in the High Court at Wellington earlier today heard evidence about Scott and wife Kylee Guy's chocolate labrador Katie and her puppies.
Three of the seven puppies that were kept in a cow shed at the Guys' Aorangi Rd home were discovered missing after Mr Guy was killed.
The Crown alleges Macdonald stole and killed three puppies to throw investigators off the trail.
Giving evidence for the third time today, Kylee Guy said her husband had given her Katie just before they were engaged and it was always the plan to breed puppies.
"She's such a beautiful dog," she said.
Mrs Guy said the puppies were seven to eight-weeks-old when her husband died.
The plan was to sell the puppies and to give one to a close friend, Joanne Moss.
Mrs Guy fought back tears as she read aloud a flier they had made offering the puppies for sale.
The flier said the purebred puppies were "looking for great homes" and were good with children.
Mrs Guy said the fliers were put up in rural stores in Feilding.
A flier was also given to Hunting and Fishing - the Palmerston North store owned by Macdonald's father - the day before Mr Guy died.
She could not recall Macdonald visiting the puppies.
Mrs Guy said she was "shocked" when she found out the puppies were missing.
Police told the family to keep quiet about it.
"I remember we had to keep it quiet, we were told to keep it quiet but then it got out."
There were eight puppies in the litter but one had been given to Ms Moss before Mr Guy was killed.
Police scene guard Brian Reynolds gave evidence that he had allowed Macdonald to visit the cow shed to feed the the puppies.
"He made the comment that there were three puppies short of the number that were in there."
It was the first police knew the puppies were missing.
Mr Guy's older sister Nikki Guy said Macdonald returned from feeding the puppies the night after Mr Guy was killed in an "animated state".
He said three puppies were missing.
"He said we weren't allowed to say anything to Kylee."
Ms Guy said Macdonald told them it would upset her too much.
The family discussed theories about how the missing puppies could be linked to Mr Guy's death.
Mr Guy's father Bryan Guy had visited the puppies on the day before his son was killed.
He said Scott took him to the cow shed to show him the work he had done there. Bryan then went back to the house and said goodbye to his son.
"The last thing I said to Scott was, 'I'll see you in the morning,"' he said.
Mr Guy said police asked the family not to mention the missing puppies because they did not want information that could help the investigation made public.
"The fewer people that knew about the puppies the better, was my understanding."
Farm worker Matthew Ireland told the court he helped Mr Guy work on the cow shed where the puppies were kept.
A couple of days before Mr Guy was killed they agreed he would also get one of the puppies, a male with a white marking on its neck.
Mr Ireland was going to pay for the puppy by working it off on the farm.
He said the puppies were playful and Katie did not mind people being around them because she was more interested in her food.
She was not noisy and did not bark at people, he said.
Mr Ireland picked up his puppy after Mr Guy was killed.
"She was barking real bad when I started walking off."
He said Katie had not behaved that way around him before.
