A crash expert told a Coroner's hearing into the disappearance of John Beckenridge and his stepson Mike it was likely someone would have been behind the wheel of their car as it went off a cliff.
The 64-year-old man and 11-year-old boy went missing in March 2015.
Beckenridge's four-wheel drive was later found in the sea at the bottom of a cliff in the Catlins, but their bodies have never been found. A coroner's hearing is being held to work out if they are missing or dead.
Senior Constable Kenneth Patterson worked in the Serious Crash Investigation Unit and examined the cliff-top scene in 2015. He said tyre marks left in the grass were key to working out whether someone was inside the vehicle when it went over the edge, or if it had been set up to crash empty.
Patterson said the straight tyre marks up to the cliff's edge clearly pointed to a person being behind the steering wheel, because the rough terrain would have made it difficult for the car to do that on its own.
"We've got clear evidence of the braking towards the edge near the marker post which is very indicative of someone being inside that vehicle, and we've also got the ability for the vehicle to stay in a straight line.
"It is likely that a person was in control and in the driver's seat or applying steering input."
Mark Templeton, private investigator for Mike's family, said the family believed Beckenridge took a number of steps to make it look like a murder-suicide to put police off their track.
When officers examined the cliff scene they found two sticks lashed together like a marker near the cliff edge.
Counsel for police Deirdre Elsmore said it had been suggested the sticks were put there to show the pair where they needed to jump out of the vehicle before it drove over the cliff.
But Patterson said there would not have been enough time, and it would not have been possible for someone to push open the door and push themselves out of the vehicle before it went over the cliff's edge.
"They would have to, within an instant, assume the velocity of that vehicle, otherwise they would most likely trip, fall and tumble. If the vehicle is travelling at a minimum speed of 45 kilometres per hour I don't think anyone can assume that velocity on landing."
Elsmore said police thought Beckenridge lacked the ability to successfully fake a murder-suicide, and that he and Mike were dead.
But Templeton said the boy's family were convinced the pair were alive and living overseas under assumed identities.
The hearing before Coroner Marcus Elliot continues.