Olivia Hope's father says it's a long shot that a photo of a woman is his daughter after she went missing, as claimed by a group maintaining she and Ben Smart were killed after being on a ketch skippered by drug smugglers.
Scott Watson was convicted of murdering the pair in the Marlborough Sounds in 1998.
A decade-old report written by the Maritime Research Group contends otherwise, suggesting Mr Smart, 21, and Ms Hope, 17, were killed after spending the night on a ketch skippered by members of a drug smuggling cartel.
The newly uncovered document contains a grainy photo of a woman said to resemble Ms Hope, taken four days after she and Mr Smart went missing.
Olivia Hope's father, Gerald Hope, has told ONE News he saw a copy of the report in 2011 and it was unclear whether the person in the grainy photo was his daughter.
"With the photo it's impossible to tell from the resolution the identity of the person. It's such a long shot," he said.
Mr Hope described the theory the report put forward as "possible but improbable" and said it was not something he took too seriously.
"I don't think there's sufficient evidence," he said.
The report's lead author, Warwick Jenness, said the photo was not an integral part of the group's theory, which was presented to police in 2006-07.
Keith Hunter, who contributed to the report, believes the pair wound up on a ketch that arrived in New Plymouth from the Pacific, going on to visit Nelson and Mapua and Queen Charlotte Sound.
"That ketch came here, it had two masts and not one, it wasn't a little boat called Blade. There's a very good chance it was connected with a drug importing operation and then it went away again," he said.
"These guys, who weren't very nice, were looking for a woman for the night. They got Olivia and they got Ben as well."
Mr Jenness said an artist's impression of the mystery ketch, included in the report, was refined using evidence from 52 witnesses.
"These witnesses included professional skippers, a tug master, a master mariner, harbour master, boat builder, charter operators, a coast watch officer and a recognised maritime historian, as well as a number of experienced yachties."
A police spokesperson said investigators were aware of the Maritime Research Group and their theories regarding the case.
"We have received various correspondence from them which has been reviewed. There is nothing in their correspondence that convinces police that anyone other than Scott Watson was responsible for the deaths of Ben Smart and Olivia Hope."