The family of 11-year-old Mike Zhao-Beckenridge have pleaded with the Coroner to keep the case open so international monitoring of the pair can continue.
This would include facial recognition which was activated along with an arrest warrant for the boy's stepfather, John Beckenridge, when the pair went missing in 2015.
A coronial hearing into the pair's disappearance will determine if they are dead, or missing.
Mike Zhao-Beckenridge would be 20 years old today. He hasn't been seen or heard from for eight years but his family believes he is alive.
"It would be too dangerous to conclude that John and Mike are deceased as all international monitoring would cease which is exactly what John wanted to happen," private investigator Mark Templeman said.
When John Beckenridge broke a parenting order and abducted his stepson from school on March 13, 2015, an Interpol red alert was loaded, barring them from leaving the country.
The pair travelled to the Catlins where they left a trail of only a few belongings and plenty of questions.
"This is a man who is angry, he has been humiliated. I think it's a final act of spite to the people behind not knowing what really happened," counsel for NZ Police Deirdre Elsmore said.
Coroner Marcus Elliot has presided over two weeks of evidence. The case is entirely circumstantial - there are no bodies - but he must rule whether the pair are dead or missing.
"The Police submission as you are aware is that both men died by murder-suicide in 2015 when John Beckenridge drove off the cliff in Blue Cod Bay," Elsmore said.
Police urged the Coroner to consider John's state of mind, his financial strife and a psychologist's evidence that he was deeply depressed.
The pair's belongings washed up at Blue Cod Bay. John's VW Touareg was found in the water, the seatbelts still firmly latched.
"The police theory is that they were sitting on the seats... and Beckenridge's intention is to die and to leave question marks. He doesn't want to risk the chance that he and Mike are found latched into their seats," Elsmore said.
On the sheer cliff above were tyre marks, a stake marking a point in the ground, two tea bags and a toothbrush.
Mike's family believes the scene was all a set-up.
"It is most likely that John and Mike Beckenridge have escaped from New Zealand by taking passage on a yacht. John is an experienced yachtsman and knows the sea well," Templeman said.
The family also pointed to John's calendar - suggesting it was unlikely to be counting down to a murder/suicide.
Deciding what happened on that day is now in the hands of the Coroner.
