However, Scott's father Brian Guy said he knew nothing of the mystery calls and said anything that could shed new light on the case needed investigation.
"Well, I would hope if police had new information they would be investigating that and yes, of course, I would support that," he said.
Scott Guy, 31, was shot at close range in the driveway of his Feilding farm on July 8, 2010.
Nine months later, his brother-in-law and business partner Ewen Macdonald was charged with murder.
But in July 2012 a jury in the Wellington High Court found him not guilty.
Macdonald's father, Kerry Macdonald, told the Herald on Sunday: "There's quite a lot that needs re-investigating.
"Ewen was found not guilty and that was 2 years ago so we've moved on - but it's really to find Scott's killer. It's not to exonerate Ewen in our view. It's more to find the killer."
Shortly after the trial, the Sensible Sentencing Trust approached four private investigators in a bid to bring Scott's killer to justice.
The team has uncovered calls from a mystery phone number to Scott Guy on the eve of his slaying. They believe he received another call from the unidentified number on the day of his death.
Investigator Mike Crawford said the evidence provided by police was "incomplete ... text messages were not there, there was an absence of cell-site data and three numbers did not have subscriber details attributed".
"We asked for raw telecommunications data from the cellphone sites in the area. The police came back and told me they never got that data, they overlooked it. I mean that is crucial evidence especially in a small rural area. You would then be able to see the phone numbers, who was texting or leaving messages - they never did that."
The private investigators have forwarded all records of phone calls and texts to Scott Guy's cellphone in the weeks leading up to, and on the day of his death, to UK-base intelligence analyst Mark Herrick.
Superintendent Sue Schwalger, who headed the police investigation, confirmed the farmer received texts and phone messages on the eve of his slaying. References to some messages and texts received by Scott Guy before his death were mentioned during Macdonald's trial.
When asked specifically about the three mystery calls, Schwalger said: "We can only answer those additional questions by referring to the file. Furthermore there has been no clarification or additional information sought from police in recent times by private investigators about information which has previously been supplied to them."
She added: "Police would welcome discussing with the private investigators any concerns or additional information they may have."
The file remained open and police were interested in any new information about the death, she said.
Crawford said after their probing, he and his team believe the main offender in the Scott Guy murder may have had an accomplice.
After the jury found Macdonald not guilty of murder, police admitted they had no other suspect.
Crawford and his team believe there are still new lines of inquiry to be explored, but they are hamstrung because of a lack of funding.
Two months after he was found not guilty of Guy's killing, Macdonald was found guilty of damage to Scott and Kylee's property and other crimes and was jailed for five years, but is set to seek parole for a third time in November.
