Scott Watson's guilt is the subject of a new book out today.

LISTEN ABOVE: NZ Herald reporter David Fisher speaks to Mike Hosking about the book

'Elementary' by controversial investigative journalist Ian Wishart advances the case that Watson and another person were involved in the 1998 murders of Ben Smart and Olivia Hope.

Ian Wishart will join Leighton Smith at 10.00am on Newstalk ZB

The theory's based on witness statements in the police file.

The NZ Herald's David Fisher said the book is a direct challenge to other books that've made a case for Watson's innocence.

Live Chat, Friday 11:30 am: David Fisher on the Sounds murders

"Ian Wishart's attacking those authors in a number of places through the book, it's a very aggressive case for Scott Watson's guilt."

Mr Fisher said the image of Scott Watson as man wrongfully convicted is set to get a shake up as the book provides a harsher look at Watson than even police put forward in the trial.

"There is an image of Scott Watson that has been portrayed of someone who was a normal kiwi guy put in the wrong place at the wrong time and stitched up by the cops. This book gives the Scott Watson image a real dust up."

He also thinks police could be left red-faced today when the book based on Watson's police file is released.

"It will cause them some discomfort to have the very internal notes of what they did made public."

Mr Fisher says he knows how the file got out and it's not the fault of the police.