Publisher Ian Wishart says a new book will finally solve the infamous Marlborough Sounds murder case.

Wishart will next week publish the book, Elementary -- The Explosive File on Scott Watson and the Disappearance of Ben and Olivia. The book looks at the disappearance of Ben Smart, 21, and Olivia Hope, 17, in the Marlborough Sounds on New Year's Day, 1998.

Scott Watson was convicted of their murders in May 1999 and remains in prison. He has denied any involvement in their disappearance and death.

The remains of Smart and Hope have never been found.

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Wishart said he was "pitching" the book as "solving the case".

"Finally we know the truth, solving an 18-year-long mystery," he told the Herald on Sunday.

Wishart yesterday released a promotional video for the book on YouTube.

He also distributed a press release stating: "A new book on the controversial Scott Watson case will be released on Friday, with never-before published information on the killings and what happened to Ben and Olivia.

"A news conference will be scheduled for Friday morning, and details will be provided this week.

"No further information is being released at this point, beyond what is contained in a video trailer that went live this afternoon."

Late last year Watson gave his first interview from behind bars.

In the North and South feature, he said: "I don't know where Ben and Olivia are. I've never met them, never seen them.

"They definitely never came on my boat and I definitely didn't murder them. And they've basically dumped me in jail for half my lifetime, it must be coming up, for something I haven't done."