In May 1999, Watson was sentenced to life imprisonment and has been in jail since. But he has always professed his innocence.
In 2007, Olivia's father Gerald Hope told the Herald he had growing doubts about whether Watson was guilty and would help fight to free the convicted killer if he was convinced of Watson's innocence.
Now Facebook group "Free Scott Watson - he is innocent", is appealing for funds to help Watson and his family "as he takes his next legal step, which will likely be another appeal to the Governor General for the exercise of the Royal Prerogative of Mercy".
For this to be granted, the Governor General will act on the advice of the Minister of Justice, and has the power to grant a pardon, reduce a sentence, or refer a case back to the courts for reconsideration.
"Many New Zealanders are concerned about the wrongful imprisonment of Scott Watson," the Givealittle page reads.
"Fighting this miscarriage of justice has cost the Watson family immensely, both financially and in other ways."
All funds raised will go to the Watson family. This morning, $555 had been raised from nine donors since the page was created yesterday.
In 2000 Watson's appeal to the Court of Appeal was unsuccessful, and in 2003 the Privy Council declined an application for leave to appeal.
In 2008 he applied to the Governor General for a royal pardon, and a QC was appointed to re-interview key witnesses, but in 2013 his application was declined.
This year, a Corrections decision to block a behind-bars meeting with North & South journalist Mike White was quashed.
In this month's issue of the magazine, Watson spoke with White, maintaining his innocence.
"I don't know where Ben and Olivia are," Watson told the magazine.
"I've never met them, never seen them. They definitely never came on my boat and I definitely didn't murder them. And they've basically dumped me in jail for half my lifetime, it must be coming up, for something I haven't done. It's destroyed my family and my life."
