The Crown accepts the diagnosis that Teina Pora suffers Foetal Alcohol Spectrum Disorder but disputes that and other admissible new evidence would have led to a not guilty verdict, the Privy Council in London heard last night.
Solicitor-General Michael Heron, QC, said he believed some expert evidence was inadmissible because it strayed into the jury's territory by stating an opinion on the truth or falsity of Pora's confession.
He suggested that other evidence about Pora's mental shortcomings would have been apparent to the jury that convicted him on retrial in 2000 of the rape and murder of Susan Burdett and that the Crown may wish to challenge the expert evidence through cross-examination.
Jonathan Krebs, for Pora, told the panel that the Crown had not provided expert scientific evidence of its own to challenge these witnesses and so there was no scientific dispute put before the panel of the Judicial Committee of the Privy Council.
The panel - made up of New Zealand's chief justice, Dame Sian Elias, and Lord Kerr, Lord Hughes, Lord Reed and Lord Toulson - discussed possible outcomes including quashing the convictions and recommending a retrial, or referring it to the Court of Appeal without quashing the convictions for the expert witnesses to be cross-examined.
Mr Krebs said he would strenuously resist the later while Mr Heron said if Pora's convictions were quashed the decision about a retrial fell to him as Solicitor-General and he would consider factors including public interest and fairness to Pora, who was released on parole in March after spending 21 years in prison.
The hearing finished after 2.5 hours on the second day. A decision is expected in January.
On the first day the panel was told by Pora's lawyers that Pora had been diagnosed with Foetal Alcohol Spectrum Disorder and had a mental age of nine or 10 years for the purpose of understanding and verbal skills. The consequences for Pora were a high degree of suggestibility, a tendency to be easily confused and a drive to please others.
This was said to be relevant because the two juries that convicted Pora assessed his confessions as though they were made "by a cogent and mature person".
Pora's lawyers also argued that an error in not calling evidence regarding the erectile dysfunction of a serial rapist Malcolm Rewa caused Pora to be wrongly convicted.
But for counsel error at the time, evidence could have been given by a majority of the 24 of Rewa's surviving victims to show Rewa suffered embarrassment because of this impairment and was therefore unlikely to take an accomplice.
Rewa was convicted of Ms Burdett's rape after semen from the scene was linked to him but two juries could not decide whether he murdered her.
The Crown argued that Pora's confessions were supported by "special knowledge" he had about the crime and corroborative evidence including witnesses who said they had seen Pora and Rewa together. All of these aspects are challenged by Pora's lawyers.
Pora was represented by Mr Krebs, Ingrid Squire and Dr Malcolm Birdling.
The Crown was represented by Mr Heron, Dr Mathew Downs and Zoe Hamill.
Mr Krebs said the appeal to the Privy Council was quite possibly the last New Zealand case to go before the court.
"It's the end of a long and distinguished association between this court and our country which began in 1847, which, I think I can speak on behalf of the Bar [Association] in New Zealand, we are very grateful.
"I want to mark, please, the feelings we have that go out for the family of Susan Burdett - it's very important that the safety of this conviction is discussed in the forum that we've just done and it can't be easy having the circumstances of her tragic death being ventilated again and again in the media as has been done, but I know, from discussions with at least one of her family members that they understand the need for what's occurred."
• Would fresh expert opinion that Pora made a false confession along with new evidence that he suffers from foetal alcohol spectrum disorder have made a difference to the verdict?
• Would the jury have reached a different conclusion had it known that Malcolm Rewa (convicted of raping Susan Burdett) suffered from erectile dysfunction?