Convicted double murderer Scott Watson has filed a new appeal, claiming a new "in-depth" forensic report challenges crucial evidence that led to his infamous conviction.
Watson was jailed for life after he was found guilty of murdering Ben Smart and Olivia Hope on New Year's Day in 1998.
Smart, 21 and Hope, 17, went missing after attending a New Year's Eve party in the Marlborough Sounds.
Watson has always denied murdering the pair and maintains he never even met them.
Much of the evidence used to convict Watson was circumstantial.
The only physical evidence police presented that linked Watson to the young couple was two blonde hairs that were believed to be Hope's which were found on his sloop following the high-profile disappearance.
Fairfax revealed today that a new appeal - an application for a Royal Prerogative of Mercy - has been filed on Watson's behalf to Governor-General Dame Patsy Reddy.
The appeal centres around a report by a forensic scientist which challenges whether the hairs found on the sloop belonged to Hope.
The report by Sean Doyle, who according to his website has more than 40 years' experience as a forensic scientist and who has provided expert evidence in major trials including Mark Lundy's, is also said to criticise the way police handled the evidence in the Sounds case.
Doyle's report spans 22 pages and concludes that there were "weaknesses" in the way ESR handled and identified the hairs, Fairfax reported.
"The hair and DNA evidence falls some way short of current standards and, in some respects, fell short of standards at the time," Doyle said.
"If adduced today, the reliability of that evidence would be strongly challenged."
Auckland man Brian McDonald is behind the appeal.
He met with Watson earlier this year after researching the case, Fairfax reported, and helped to raise the funds needed for Doyle to compile the forensic report.
"The new evidence focuses on the how the hair samples were mishandled and how the evidence can't be looked at in isolation," McDonald told Fairfax.
He hoped the report would push the government to order a retrial for Watson, arguably one of the country's most controversial killers, or quash his conviction entirely.
Watson and his father Chris had both read the forensic report.
Chris Watson confirmed the report to the Herald this morning.
He believed it could go some way in helping with a retrial or acquittal for his son.
"The fall-back position on new bits of evidence - and this is new evidence - was always 'but it's the hairs', and Brian McDonald has attacked the hairs pretty much," he said.
However, he said the report still representing "just another wait and another kick in the teeth".
"My hopes depend on the Criminal Cases Review Commission," he said. "The Justice Department is going to defend itself, Brian is prepared to take this further if he has to."
Watson told Fairfax he and his son both backed the appeal.
"Scott is optimistic, hopeful, with a touch of pessimism about the whole thing," he said.
"He is getting on with life, he has got a lot to get along with."
Chris Watson and his inmate son filed an application for a Royal Prerogative of Mercy in 2009.
But after receiving advice from then-Justice Minister Judith Collins, the Governor-General denied the request.
Watson has also appealed to the Court of Appeal and the Privy Council.
Those attempts were also unsuccessful.