Hundreds of pieces of evidence point to Scott Watson as the murderer of Ben Smart and Olivia Hope, the Court of Appeal has been told.
Watson is attempting to overturn his convictions for the murders in the Marlborough Sounds on New Year's Day 1998.
His lawyers have argued the case against him depended heavily on a tainted eye-witness identification and flawed DNA analysis of two hairs linked to Olivia Hope.
But Crown prosecutor Madeleine Laracy said that was a mischaracterisation of the original case.
Over the three-month trial, the jury heard from 480 witnesses and was presented with hundreds of interlinking pieces of evidence, which showed Watson was the only person with the motive, opportunity and propensity to commit the murders, she said.
The Crown prosecutor in the original trial, Paul Davison QC, started his closing address by "asking the jury to stand back and consider in the abstract the necessary characteristics" of whoever committed the murders, she told the court.
The killer must have been a male, a lone man, a stranger to Smart and Hope, had "pre-existing intent or willingness to kill", a pre-existing relevant motive ("you don't just develop murderous intent out of thin air at a party"), must have had a yacht in "the relevant area of Furneaux Lodge" and must have been onshore at the exact time of Guy Wallace's water taxi trip.
Wallace dropped the young pair off at the stranger's yacht after he offered them a berth.
The Crown's case rested on the "singular motive required in combination with the exclusion of any other person on all of the evidence who fitted the criteria", Laracy said.
"Scott Watson had the motive - to secure a woman for the night - the opportunity (Olivia appeared) and the opportunity to dispose of the bodies."
Furthermore, his actions and behaviour on New Year's Eve and New Year's Day were strongly suggestive of someone trying to cover his tracks, she said.
"His conduct from daybreak was strongly suggestive of someone intent on avoiding detection and getting rid of evidence."
Looked at "fairly, objectively and in its totality", the evidence pointed to Watson's guilt, she said.
Watson's defence team has argued the identification by Wallace should never have been put before the jury, because it was so tainted by the other photographs he had been shown by both police and the media. They said Watson's lawyers at the first trial never had that information about the police photo.
However, another Crown lawyer, Stuart Baker, presented letters from Crown Law at the time showing documents pertaining to the photo were included in the original disclosure documents. Therefore, Watson's defence did have access to that information - but for whatever reason, did not use it.
Baker noted the defence was not claiming there had been an error in the original defence.
Furthermore, he said there was no way of knowing whether that photo influenced Wallace's later positive identification of Watson.
RNZ
