Mr Guy, 31, was gunned down in the driveway of his rural Feilding home in the early hours of July 8, 2010 as he set out to do the milking.
The jury trial of his brother-in-law Ewen Macdonald, 32, began in the High Court at Wellington today.
The Crown alleges Macdonald shot Mr Guy at close range in the throat with a shotgun from the family farm, and then shot him a second time in the arm and hand.
Truck driver David Berry, who lived further up from Mr Guy on Aorangi Rd, told the jury he noticed the lights on Mr Guy's ute were on when he drove past shortly after 7am.
"It was quite awkward to see because the lights were shining at me as I went past,'' he said.
Mr Berry then noticed Mr Guy's boots in the driveway.
"That's when I slammed the brakes on.''
He reversed his large truck and got out to see Mr Guy lying in the driveway in front of his ute.
The ute was still running and its driver's door was open.
At first Mr Berry thought Mr Guy had been knocked over by stock, but he tried to feel for his pulse.
"He was quite cold.''
He then noticed Mr Guy's injuries and blood around his body.
"I thought he'd had his throat cut.''
Mr Berry said he did not touch the body again and went back to his truck to call police.
His evidence will continue tomorrow.
The jury earlier heard from Simon Asplin, the assistant manager on the farm that Mr Guy co-managed with Macdonald, who is married to Mr Guy's sister Anna.
Mr Asplin told the jury that he and Macdonald had referred to Mr Guy as "Sleeping Beauty'' when he did not show up for milking that morning.
Mr Guy had been expected to arrive first to milk the cows that morning.
"We just had an in-house joke that Sleeping Beauty was Scott,'' Mr Asplin said.
When Mr Guy did not show, Mr Asplin, Macdonald and farm worker Matthew Ireland continued to milk the cows as usual without him.
Mr Asplin said Macdonald later called Mr Guy.
"I think I asked if Ewen had rung to find out where he was, and he said he had.''
Macdonald had told him the call went to answerphone.
Mr Asplin did not know anything had happened to Mr Guy until later in the morning when Macdonald called to tell him Mr Guy had been "involved in an accident''.
Mr Ireland later told him that Mr Guy had been shot dead.
Under cross-examination by defence lawyer Greg King, Mr Asplin conceded he often did not get along with Mr Guy.
When a friend asked why anyone would want to kill Mr Guy, Mr Asplin said he had raised his voice "because I was upset''.
He agreed he later told another person that one good thing had come out of Mr Guy's death - that he would be able to spend more time on the tractor, which he had done less of since Mr Guy became co-manager of the farm.
Mr King also questioned Mr Asplin over how he knew Mr Guy had been shot.
He said Mr Ireland had told him, but Mr King said Mr Ireland had denied that to police.
Mr King said: "You hated Scott Guy, didn't you.''
Mr Asplin denied that, saying he didn't get along with him sometimes. "But I didn't hate him.''
Crown prosecutor Ben Vanderkolk earlier said Macdonald had trapped Mr Guy at the end of his driveway by closing the farm gates on the morning he was killed.
When Mr Guy got out of his ute to open the gates, Macdonald was waiting in the dark by the farm fence.
"The killer must have stepped out of the darkness, illuminated by the lights as he just stepped into the beam,'' Mr Vanderkolk said.
He said the jury would hear evidence that shoe impressions found around the fence and gate matched those of a pair of Proline diving boots that Macdonald later disposed of.
The shoe impressions also led to an area on Mr Guy's property where a labrador and seven of its puppies were kept.
Mr Vanderkolk said Macdonald had killed three of the puppies.
Mr King said Mr Guy had been murdered, but it was not his client that had done it.
He described the case as a "proverbial and classic whodunit, a murder mystery''.
Mr King said the timing of events on the morning of July 8 would be "critical'' to the case.
The trial is set down for six weeks and dozens of witnesses, including members of the Guy family, are expected to be called.
