The validity of scientific evidence was argued on the first day of an appeal by convicted double murderer Mark Lundy at the Privy Council in London.
Four British justices and New Zealand Chief Justice Dame Sian Elias are hearing the appeal against Lundy's conviction for the murder of his wife, Christine, 38, and Amber,7, in Palmerston North 13 years ago.
Lundy was arrested six months later and sentenced to prison in 2002 for 17 years after being found guilty of double murder.
The Court of Appeal later extended his sentence to 20 years.
Lawyer David Hislop, QC, said crucial evidence by American pathologist Rodney Miller was flawed and that Lundy's trial counsel had relied on experts using questionable science.
That evidence related to DNA, said to be his wife's brain tissue, found on a shirt belonging to Lundy.
Mr Hislop also suggested that some evidence from other Crown experts, which conflicted with Dr Miller's, was not disclosed to the defence.