The Court of Appeal begins a second appeal into the Scott Watson murder case, today.  

Friends Ben Smart and Olivia Hope were last seen getting off a water taxi onto a yacht in the Marlborough Sounds on New Year's Eve more than 26 years ago.  

Watson was convicted of double-murder in 1999 following a three-month jury trial in the High Court in Wellington.  

It's accepted the pair met their deaths after boarding a stranger's yacht with a man -- the Crown says that man was Watson.  

Watson's always denied killing or even meeting them. This appeal is of his conviction -- and Watson's team can include new expert evidence about the reliability of forensic evidence. 

Criminal defence lawyer John Munro told Mike Hosking “Transference of DNZ is much more understandable now, so is hairs.” 

Munro said the key issue is whether he’s had a fair trial. It won't just ‘turn on the hairs’ – the judge will focus on whether he was in fact spotted on water taxi. 

LISTEN ABOVE.