The families of Ben Smart and Olivia Hope describe the man convicted of killing the two young people as "innately evil" and "rehearsed" in his claims of innocence.
On New Year's Day, it will be 20 years since Ben and Olivia were last seen alive climbing onto a yacht with a "mystery man".
The "mystery man" was Scott Watson, according to the police who charged him with murdering the two young people - and the jury who found him guilty in 1999.
Since then, doubts have been raised regularly about the circumstantial evidence but Watson has failed in several attempts to quash his convictions.
To mark the 20 years since Ben and Olivia disappeared, the Herald has launched Chasing Ghosts: Murder in the Sounds - a three-part podcast, feature story and video series - to examine one of New Zealand's most enduring mysteries.
It comes as Watson, now 46, makes another bid for freedom with a second application for a royal pardon.
His father Chris is adamant his son had nothing to do with the deaths of Ben, 21, and Olivia, 17.
"I know he didn't [kill them]," says Chris Watson. "And not from anything he's told me. I've looked at it and used my intelligence and commonsense."
But Ben's mother, Mary Smart, is convinced the police got the right man.
I think he is innately evil. I don't think he should be let out.
And there is a daily reminder of her son's disappearance.
Watson's boat Blade - where he supposedly murdered the pair, before dumping the bodies at sea - can be seen from her Waikawa Bay home, moored less than 100 metres away.
She declined an interview with the Herald as the 20 years since Ben disappeared was not an anniversary - there's nothing to celebrate.
"It's something very sad to think what would he be doing now," Mrs Smart says of Ben.
"He would probably be married with children and things like that, you think about. But nobody wants to talk about it anymore."
Gerald Hope, who for many years questioned the evidence against Watson, met the man convicted of killing his daughter. He now believes Watson's explanations were "rehearsed" and "insincere".
"There has been so much of our lives taken up with this and there is nothing more for us to say."
However, others whose lives were swept up in the police investigation - including crucial witnesses - say Scott Watson is innocent.
"I know if Scott wasn't in there, I would be in there," Guy Wallace says.
"Because they just had to get someone. It's as simple as that."