The eyewitness whose identification of Scott Watson was crucial in convicting him for double murder had a weak memory which was contaminated, an expert in identification has told the Court of Appeal.

It’s the first day of Watson’s week-long appeal hearing in Wellington before judges Christine French, Susan Thomas and Patricia Courtney.

He was found guilty in 1999 of murdering Ben Smart and Olivia Hope in the Marlborough Sounds. He’s been in jail for nearly 25 years and has always maintained he’s innocent.

Emeritus Professor Gary Wells, an expert in eyewitness identification from Iowa University, is giving evidence on his report, which casts doubt on how accurately the late Guy Wallace identified Watson.

Wallace was the water taxi driver who took Smart, Hope and a third man to a yacht following a 1997 New Year’s Eve party. It was the last time Smart and Hope were ever seen.

Wells told the court Wallace’s identification of Watson as the man had “no probative value” because of Wallace’s “early rejections” of photos he was shown of Watson.

He said his later identification from a montage of six other photographs was “wavering” and “non-confident.”

The first photograph Wallace was shown of Watson was a black and white picture from 1990. He told the court Wallace’s rejection was “explicit”, saying there was “no bloody way” it was the man he’d transported.

One of New Zealand’s most high-profile and controversial murder cases is back before the courts this week, as Scott Watson challenges his convictions for the murders of Ben Smart and Olivia Hope in the Marlborough Sounds in 1998.

Wells said Wallace rejected another photograph in “montage A”, but the Crown disputes he was ever shown that.

It was from “montage B” some months later that Wallace identified Watson, but Wells said he wavered between photograph three and five for some time. Photograph three was Watson.

“But remember, he’s seen him multiple, multiple times in media…..It ought to be easy by that point and that he’s still struggling between three and five.”

“And I think that’s because he’s having trouble reconciling that with his memory.”

“His memory goes back to what he described and depicted in his composite while his memory was still fresh,” Wells told the court.

Wallace’s initial description of the man he saw on the boat was that he had long, scraggly hair. Wells said he stuck consistently to that and endorsed a composite drawing that resembled his description.

‘It’s not coming from memory’

Wells also questioned the reliability of Hope’ sister Amelia’s description of the mystery man.

He said she never brought up short hair in her initial statement, but after Watson was presented as suspect on TVNZ news she mentioned short hair and a receding hair line.

“It’s you picking up what we call post event information. It’s not coming from memory…. it’s coming from information acquired later on through other sources,” he told the court.

Under cross-examination from crown lawyer Stuart Barker, Wells said he was not an advocate for Watson and he wasn’t saying he was innocent.

“I don’t care about Mr. Watson. I didn’t know, even know about this case….. But I do want eyewitness evidence interpreted correctly.”

The hearing continues.