Scott Watson is being allowed to challenge key eyewitness evidence during his appeal for his conviction for murdering Ben Smart and Olivia Hope.
Watson was convicted of murdering Smart and Hope, whose bodies were never found, in the Marlborough Sounds in 1998.
The pair was last seen getting off a water taxi in the early hours of January 1, 1998. Watson, now 50, was sentenced to life in prison and has spent 24 years behind bars. He has always denied killing the pair whose bodies were never found.
In a decision released on Wednesday, the Court of Appeals ruled Watson can challenge whether the identification of him being the mystery man who was last seen with the pair was properly obtained and therefore able to be heard by the jury during his trial.
Watson was identified as the mystery man last seen with Smart and Hope by the water taxi driver Guy Wallace. Wallace identified Watson based on a photo montage shown to him by police. However, there is controversy surrounding the montage because it pictured Watson mid-blink, which matched other descriptions that said the mystery man had hooded eyes.
In its release, the Court of Appeals said Watson could challenge the montage in his upcoming appeal.
"If there is one lesson from the history of miscarriage of justice in the context of criminal appeals, it is that no good is done by the procedural suppression of a tenable ground of appeal which has not yet seen the light of day in an appellate court, while other grounds of appeal are nonetheless allowed to proceed," former Court of Appeal President Stephen Kos noted in the ruling.
Along with the photo montage, Watson will be challenging the legitimacy of two hairs that were found on his yacht and matched to Hope.
The hairs play a central role in the case and Watson's team argue the forensic testing was unreliable.
Watson has already been denied parole four times - partly due to his refusal to admit guilt. His Court of Appeal hearing will take place on August 31.
After the trial, Wallace, who died in 2021, said he didn't believe Watson was the man he saw with Smart and Hope.
