The jury at Mark Lundy's retrial was drowning in a sea of science, his lawyers have told the Court of Appeal.
The man who has twice been found guilty of murdering his wife, Christine and daughter, Amber, has taken a case there in an effort to have his 2015 convictions overturned.
The bodies of 38-year-old Christine Lundy and 7-year-old Amber were found by Mrs Lundy's brother in their Palmerston North home on 30 August 2000. Both had been bludgeoned to death.
An important part of the Crown's case at the retrial was the scientific RNA evidence. RNA is similar to DNA but allows a scientist to pinpoint which part of the body a particular piece of tissue is from.
Both the Crown and Defence called scientific experts to give evidence on that at the retrial, primarily in relation to a stain found on his shirt, which was said to contain some of Christine Lundy's brain tissue.
Mark Lundy's lawyer Jonathan Eaton told the Court of Appeal today that an earlier Court decision allowing that evidence to go before the jury, stated "the jury will not be drowning in a sea of science".
However, that was exactly what happened at the retrial, he said.
"The jury had to choose which scientist they liked best and may have decided they preferred the Crown's; and it may have been based, not on true reliability and weight [of evidence], but rather on the impression they had of each scientist."
Mr Eaton said the jurors were effectively asked to sit in peer review of the scientific evidence.
He said that was the only issue which had its own handout in the material given to the jury.
"[That was] six pages and in summing up the trial judge suggested the jury might start [its deliberations] with that evidence."
The case is continuing and the Crown's submissions are likely to begin later today.