Scott Watson is attempting to overturn his conviction for the murders of Olivia Hope and Ben Smart. Photo: Pool / John Kirk-Anderson
Two blonde hairs linked to murder victim Olivia Hope have come under the microscope in the Court of Appeal.
Scott Watson is attempting to overturn his convictions for the murders of Hope, who was 17, and Ben Smart, 21 after a New Year's Eve party in the Marlborough Sounds in 1998.
In the absence of a smoking gun or any murder weapon - or even a body for that matter - the original case against Scott Watson put a lot of weight on two blonde hairs found on his boat.
However, how they came to be on the boat, or whether in fact they made it onto the boat at all, or got mixed up in the lab, is the cause of ongoing debate, and a key reason why the case has ended up in the Court of Appeal.
The two blonde hairs were found in a bag of hairs taken from a tiger print blanket on board Watson's boat, Blade.
Forensic scientist Paige McElhinney, who reviewed the forensic examination for the defence, said the court could not exclude the possibility that hairs were taken on board Blade by police by accident.
"We know that PPE [personal protective equipment] was worn but it's what they did while wearing the PPE.
"In past scene examinations that I've been at, it's been 'Let's all sit in the car and have lunch' with overalls tied around the waist.
"So it's beyond just PPE was worn, but how was it worn? Was it changed daily or every time they got off [the boat] and got back on?
"That information isn't there."
McElhinney said it was also possible - as ESR forensic scientist Susan Vintiner conceded at trial - that the hairs could have got to Watson' boat by "transference", picked up on his clothing at the party.
It was also possible that hairs collected from Olivia's bedroom for comparison purposes could have come out of the bag (which was found at trial to have a slit in it) and found their way into the bag of hairs taken from Blade in the lab.
The steps taken by Susan Vintiner that she described in her affidavit - disinfecting the area, changing the paper on the bench, disposing of her gloves - would have minimised the risk of contamination, she said.
"She would have been aware of those possibilities.
"But we're also just human and errors can happen."
Susan Vintiner was asked by defence lawyer Nick Chisnall whether she should have been more clear with the jury at the original trial about the possibility of transference.
"No, I don't accept that," she replied.
"Because I believe when I was asked if it was a possibility by Mr Davidson [Scott Watson's lawyer at the first trial, Bruce Davidson], I agreed with him that yes, the jury should consider this."
Under cross examination, Vintiner said she did not know how the bag containing the hair was perforated, and admitted it may have been present when she made her initial examination.
Earlier on Tuesday the Court of Appeal was told forensic scientist who examined two hairs did not use standard operating procedures.
Forensic scientist Sean Doyle, who prepared several reports for Watson's defence team said that the scientist who examined the hairs used her "personal preferences" in her approach.
Furthermore, there was nothing in her notes from the time to support what she said in her affidavit about the methods she used, he said.
"My expectation would be today that the procedure she used would actually be in the SOP (standard operating procedure) and it wasn't.
"And because she's using her own personal judgement, I would expect a detailed record to be made and certainly recording what she actually did in terms of 'I cut the bag open, I put the tweezers in and I pulled the hair out'.
"It's surprising to me that it doesn't appear, at least I can't find it in the case files, and I think that's a very significant piece of information."
One of the panel members, Justice Susan Thomas, asked Doyle what he would have expected in terms of records "at the time".
"The world was a very different place in 1998," he replied.
"But because she is exercising personal preference and because they do have a hair examination SOP [at the laboratory] that makes no mention whatsoever of this sampling technique, it was surprising to me even at that time that there wasn't a detailed record and that the SOP didn't include the option that she took as her sampling procedure."
Crown lawyer Robin McCoubrey told Doyle suggesting in his report that the use of personal preferences by a scientist indicated a laboratory system "not fully under control", was "designed to scare the reader".
However, Doyle repeated his assertion that he would have expected the method used to be recorded at the time so that another scientist could reproduce those results.
McCoubrey said the risk of contamination and transference in the hair samples were both raised as possibilities at trial.
He quoted the judge at the time as saying "It's not trial by scientist, it's trial by jury".
"This risk is nothing new is it?"
Doyle agreed it was for the jury to consider the scientific evidence and concessions made during cross-examination.