The parents of Ben Smart say they do not agree with doubts expressed by Gerald Hope about the conviction of Scott Watson.
In a TV3 documentary screening this Thursday, Olivia's father, Gerald Hope, meets Chris Watson, father of the man found guilty of murdering the Blenheim friends.
He also boards the sloop which Ben and Olivia are said to have been on before being murdered.
Mr Hope says he is no longer convinced the events on New Year's Day 1998 happened the way the Crown depicted them.
That has put doubt on the conviction of Watson, who is serving a 17-year non-parole sentence.
For the parents of Ben Smart, the documentary and related publicity have brought the horror of four years ago back to life.
But it has not changed their opinion of the guilty verdict.
"We don't agree with Gerald on this issue," said Mary Smart. "We think differently. As far as we are concerned, it was a fair and just trial."
The Smarts declined to appear in the documentary but had been kept informed about it by the director/producer, John Keir.
Greenstone Productions, the maker of the documentary, also approached the head of the police investigation into the disappearance, Detective Inspector Rob Pope, and Olivia's mother, Jan Hope. They would not take part.
One of the major aspects of the programme is the first-ever face-to-face meeting of Gerald Hope and Chris Watson. Mr Keir said both discovered common ground.
"I think the reason both fathers agreed to take part is they both need to shake the tree and see what comes down, what's new that hasn't fallen before."
Scott Watson's mother said yesterday that it was good news that Mr Hope was now expressing doubts over the case.
Beverly Watson said it was one less person, and an influential person, they had to fight in the campaign to free their son.
Just a year ago Mr Hope attacked the Watsons, saying they were extremely misguided.
"If they can't understand their own son's evidence then I suggest they reread it ... As long as there's breath in his lungs he's got the capability of actually recanting those lies."
Mrs Watson said that if Mr Hope now had doubts he should examine the police files.
"Then he would be convinced that Scott had nothing to do with it."