The author of an explosive new book on the Marlborough Sounds murders of Olivia Hope and Ben Smart says he has proved Scott Watson "definitely lied" about his whereabouts on New Year's Day in 1998.

At a media conference this morning, Ian Wishart said his book Elementary shone new light on the character of Watson.

"The book is not about betraying Scott Watson. It's about how Scott Watson betrayed New Zealanders," he said.

Wishart believed Watson "definitely lied" about his whereabouts on the day of the murders. "The evidence is undeniable."


Wishart said Watson had a "Jekyll and Hyde" personality which was significantly affected by drinking and drug-taking.

In Wishart's opinion, this and the events of January 1, 1998, created the "perfect storm" which Ben and Olivia became unfortunate victims of.

Wishart also described elements of the Maritime Research Group report, which the Herald published yesterday theorising drug smugglers had been involved in the disappearance of the pair, as "utterly ridiculous", with "no credibility at all".

Scott Watson, right, in the High Court in Christchurch last year. Photo / Supplied
Scott Watson, right, in the High Court in Christchurch last year. Photo / Supplied

In Elementary, Wishart writes that the bodies of Ms Hope and Mr Smart were brought ashore and buried on land, in contrast to the police case which contends that they were dumped at sea.

Asked why if the evidence was so strong, it wasn't presented in court, Mr Wishart said: "Perhaps the prosecution and investigative team didn't talk to each other enough. The court trial was a dog's breakfast. People had forgotten things and Watson's team did a very good job of cross examining people."

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Wishart claimed financial motivations did not lead him to write Elementary, his second book on the Marlborough Sounds murders.

"I didn't have access to police files when the first book, Ben and Olivia, was published," he said.

"If I had then Ben and Olivia would have had a very different tone. I didn't want to have to say I had been wrong in supporting Scott Watson, but when I got access to the police files, and read what was in them, I felt the public had the right to know."

Wishart also revealed he gave Olivia's father, Gerald Hope, an advanced copy of the book because he wanted Mr Hope to be forewarned about its content and be prepared for questions media might ask.

"It seemed fair to them. Ben and Olivia's families have lived with this every single day."

Wishart said he didn't believe Watson had set out to kill Ben and Olivia but he did, and should own up to it.

"I defended you, Scott," he said.

More to follow.