Police "strongly disagree" with a number of claims made in a recent book about the disappearance of Ben Smart and Olivia Hope.
Ian Wishart's Elementary was released in January this year. While it agreed with police that Scott Watson was responsible for their murders, it made several new claims.
Ms Hope, 17, and Mr Smart, 21, disappeared after a New Year's party in 1998 and were last seen boarding a double-masted ketch afterward at Furneaux Lodge in the Marlborough Sounds.
Watson, who was also at the party, was arrested and convicted of the double-murder in 1999, though the bodies were never found. He still denies he's responsible for their deaths, and there has been an effort by others to clear his name -- Mr Wishart used to be among them.
Watson says he returned from the party alone on his single-mast boat Blade, before sailing on his own to a friend's place to paint the boat.
But a witness provided a description of the boat and said he saw two people on board -- confirmed by two other vessels.
It is also alleged there was a sighting in Erie Bay, and that Watson and an unknown accomplice removed the bodies on January 1, 1998, in Shakespeare Bay.
Police combed through the book and compared them to the original investigation file.
They still maintain Watson is responsible for the murders, but "strongly disagree" with some of Mr Wishart's claims, including that:
"While we understand the enduring public interest in this case, police are not in a position to publicly re-litigate evidence which has been gathered during a historic investigation, including evidence which was put before the court," says Detective Superintendent Peter Read.
"We are particularly mindful of our obligations of fairness and privacy around witnesses who provided information to police,"
"We can however say that we have considered each of these claims in detail, including examination of the file and witness statements taken at the time.
"We have also spoken to staff who were involved in the original investigation. As a result of this work police do not believe there is any substance to the above claims in Mr Wishart's book."
He says police rely on corroborated evidence and testimony in the prosecution case against Watson.
Supt Read says it isn't unusual for witness sightings to contradict each other.
"Police and prosecutors made decisions on who gave evidence based on corroborated accounts that were supported by the known facts."
But Mr Wishart has fired back, saying their dismissal of the evidence is "factually incorrect butt-covering".