A private investigator believes missing John Beckenridge and his stepson are still alive but no longer in New Zealand.
Eight years ago, 64-year-old Beckenridge went missing along with his 11-year-old stepson Mike.
The pair had been camping at the bottom of the South Island until they went missing. Beckenridge's four-wheel drive was later found off the Southland coast but their bodies were never found.
Now, a coronial hearing is underway in Christchurch to determine if the pair are dead.
One witness testified he had been contacted by Mike via the video game Minecraft. However, Detective Jeremy Dix told the hearing the witness was mistaken.
Mike's mother, however, was adamant the pair are still alive.
Private investigator Julia Hartley Moore, a best-selling author who's been following the coronial hearing, said the two most plausible explanations were a murder-suicide had taken place or the pair were still alive.
"[John] had the ability to probably leave [New Zealand] more than most without being caught because he was a pilot; because he probably had connections overseas," Hartley Moore told AM host Ryan Bridge on Thursday.
"We deal with people who definitely leave and they just go away without any warning; walk out the door… and disappear, that's it."
But she said those people are usually found eventually.
"This is different," she said. "[John's] taken his stepson and I think he has the ability to take it further than most people would have the ability to do so… Myself, I think they're alive but I don't think they're here."
The purpose of the ongoing hearing is for coroner Marcus Elliot to rule whether they are dead or alive. Mike's mother believes her son is still alive and his disappearance was staged by her ex-husband.
On March 13, 2015, Beckenridge breached a parenting order when he went to his stepson's school and picked him up before heading to the Catlins, an exposed area at the bottom of the South Island, where they camped at various locations.
Beckenridge's car was found at the bottom of sheer cliffs near Curio Bay in the Catlins along with other things belonging to the duo including a tent, sleeping bags and empty fuel containers at a campsite - but the pair has never been heard from nor have their bodies found.
The coroner's hearing continues.
