The investigation into missing Invercargill boy Mike Zhao-Beckenridge and his stepfather John Beckenridge will not be closed, despite police referring the case to the coroner.
A forensic examination of the car linked to the pair's disappearance has found no sign of human remains.
The vehicle was pulled from the sea near Curio Bay earlier this month after it had been submerged in rough seas for a couple of months.
Southland area commander Inspector Kelvin Lloyd yesterday said police remained ''ever hopeful'', but the treacherous seas and the condition the vehicle came out in had been ''major frustrations'' in the search.
''It's essentially left of us with a chassis, a motor and three wheels - and that's all that's been left of the vehicle,'' he said.
''We knew that it was going to be a struggle to get anything from it, but we had to do that in any case.''
Police were not following any active leads, but this was ''far from'' the end of police investigations, he said.
Officers would actively pursue any further lines of inquiry.
''We'd love to have another confirmed sighting, which would give us another avenue of inquiry, or find something that would assist with a coronial inquiry.
''Obviously, our preference would be the former, but both those things would assist.''
Insp Lloyd said police were working closely with the ''distraught'' family.
The coroner was well aware of the police investigation and police would be holding jurisdiction until they had exhausted every avenue of inquiry.
''We are ever hopeful that [Mike and his stepfather] are in the community somewhere, but the evidence that we have at the moment is not indicating that they are,'' he said.
''We've been working on behalf of the family, that's who we've been working for since day one. We're trying to get some resolution for them.''
On March 13, Mr Beckenridge (64), of Queenstown, picked Mike up from his Invercargill school in breach of a parenting order and disappeared. The last confirmed sighting of the pair was March 16.