Police are disappointed they were not able to adequately warn family over the decision to grant Mark Lundy the right to appeal his convictions for the murder of his wife and daughter.
Police found out about the Privy Council decision through the media this morning "which is unfortunate, particularly as it did not give us the opportunity to inform the victim's families first," a statement said.
A spokesman for New Zealand Police said they would meet Crown Law to consider the appeal.
Police frustrations were shared by the brother of Lundy's late wife, Christine. Glenn Weggery said he was angry to have heard the news from media outlets.
"I'm rather p***** off that victims in this country are so badly thought of that no one has the balls to inform us before the media gets hold of these things," he said.
"Even [Lundy's] supporters could have had the balls to call us. They know where we are. They don't think about the victims."
More than a decade after he was convicted of the brutal axe killing of his wife Christine and 7-year-old daughter Amber, Lundy will have an appeal heard by the Privy Council in London over three days in June.
His last-ditch appeal will focus on "the most important piece of evidence" that linked him to the killings.
London-based lawyer David Hislop QC says the defence case will focus on a "science experiment" used to identify DNA on Lundy's shirt as being his wife's brain tissue.
Mr Hislop said the crucial evidence used "flawed science" and he accused police investigating the murders of "shopping around" for an expert to give them the testimony they needed.
The expert was Texan scientist Dr Rodney Miller, who confirmed to APNZ that he had been called as a witness in the Lundy appeal.
Dr Miller refused to comment on the appeal or claims his evidence was based on "bad science", but he has previously written a paper about the importance of his evidence in which he said police had contacted "multiple forensic laboratories in New Zealand, Great Britain and the United States" before approaching him.
Mr Hislop told Radio New Zealand today that Dr Miller had never previously done the test that was used to determine whether it was Christine Lundy's brain tissue on her husband's shirt, and it used a flawed method.
"What happened in essence was the people in New Zealand weren't sure what [the DNA on Lundy's shirt] was," Mr Hislop said.
"They weren't sure, [investigators] went overseas, they shopped for an expert and of course in the US you can get all sorts of experts if you shop around, and they got one."
Mr Hislop said if Christine's DNA on her husband's shirt was not conclusively proven to be brain tissue it would not place Lundy at the crime scene.
In a paper written in 2003 about his involvement in the case, Dr Miller said "the definitive identification of brain tissue on Mark Lundy's shirt using immunohistochemistry was the most important piece of evidence pointing toward Mark Lundy's guilt".
Police would not comment on criticisms by Mr Hislop that detectives had relied on unrecognised science to charge Lundy with the murders.
Lundy is currently serving 20 years in prison for the murders.
In 2002 he lost an appeal to the Court of Appeal and had his non-parole period increased to 20 years, the longest non-parole period of imprisonment for a life sentence ever handed down in New Zealand.
The Privy Council hearing will be held over three days in the week starting June 17.
If successful, Mr Hislop said the case would likely be sent back to New Zealand where prosecutors would have to decide on a retrial.
Mr Weggery said news of the appeal was "very tough" for the family.
"It's 12 years later, we're trying to move on with our life and let Christine and Amber rest in peace and it's just not being allowed to be done," Mr Weggery told RNZ.
"It keeps getting dragged up every few months.
"He's got the right to appeal, fine. But it's been dragged out for so long, and it took so long for them to lodge their appeal when they've been talking about it for years.
"Did any of them ever care about Christine and Amber? Because they sure as hell don't care about their families."
Palmerston North residents were fuming this morning at news of Lundy's Privy Council appeal, with all those spoken to certain of his guilt.
"He's a bloody idiot," Matt Schofield told the Manawatu Guardian. "I believe he did it. I drive down there (Wellington) three times a month and if he did it in that speed, he must be a Formula 1 driver. But I still think he's just a pig and he needs to accept what he's done."
Nicolaas Mels was also unhappy at the appeal bid.
"I'm against the decision made today - he has had his chances."
Steve Swan was adamant that Lundy should remain behind bars for life. "If it was me, I would be giving him the death sentence. A mongrel like him who can kill a little girl like that - it's wrong."
- additional reporting by Alecia Bailey