UPDATE 2.45pm: Mark Lundy's lawyer has spoken of an "unidentified male" and unexplained DNA that throws doubt on the double murder conviction of his client.

Jonathan Eaton, QC, said on Tuesday at the Court of Appeal that there were 51 possible suspects identified by police in the case, but circumstantial evidence pointed to his client.

"Mr Lundy was spoken to hours after the murder, and his watch, ring, spectacles and car were all forensically tested and showed nothing.

"If he was so careful, why was there (wife Christine's) brain matter on his polo shirt? The murder was carried out in such rage but Mr Lundy drove calmly back to Wellington and saw customers the next morning.

"There was no evidence in the motel, car or house that pointed to him."

Mr Eaton said fingernail scrapings from Christine and Amber came from an "unidentified male" that was not Lundy.

Fibres also found on Christine were also from unidentified clothing and she also had hairs clutched in her hand that were not Mr Lundy's.

Mr Lundy talked with police without a lawyer, "freely and consistently", Mr Eaton said.

Lundy's original conviction, from 2002, was quashed by the Privy Council in 2013 and a retrial ordered, after which he was found guilty again.

He was sentenced to life in jail with a minimum non-parole period of 20 years.

Mr Eaton said a key part of the Crown's case was the use of "untested and novel" scientific testing that proved brain tissue on a polo shirt owned by Lundy was likely to be Christine's.

"It is extraordinary and unique that an individual has been tried on facts that are so much in dispute," he said.

Mr Eaton said Lundy was not a violent man and the assertions he travelled to Palmerston North from Wellington, and back, and committed the murders for financial gain was "implausible" and could be unravelled under scrutiny.

Lundy was not present in court.