A former judge who ruled on Teina Pora's compensation deal says it is well known that eyewitness identification evidence can be unreliable.

The Criminal Cases Review Commission Te Kāhui has launched its first systemic inquiry, which will investigate how eyewitness evidence is used to identify defendants.

Problems with identification evidence have featured in some of the country's highest-profile wrongful conviction cases.

Former high court judge Rodney Hansen was involved with compensation claims for two such cases - Teina Pora and Alan Hall - and he says eyewitness accounts were among the most persuasive evidence a prosecution could bring to court.

"The evidence from someone, whether they're independent or not, who says 'I saw so-and-so running away from the scene of the crime', for example, well that's highly compelling evidence, if the evidence is accepted."

But the King's Counsel says it's also well established that this sort of evidence can be flawed.

"People can make mistakes over identification, which is the reason why the law has for many, many years now required judges to warn juries to take the utmost care and tread with the utmost caution."

Hansen retired from the judiciary a decade ago after sitting for 14 years, but says the rules and practices around eyewitness evidence doesn't seem to have changed much since his time on the bench. Any inquiry into the eyewitness evidence can only be applauded, he says.

Hansen describes such evidence as being "a peripheral issue" in Pora's case, but says it's a significant factor for Hall - his conviction for the murder of Paul Easton was quashed after 37 years, because police hid and changed information garnered from witnesses.

Alan's brother Geoff Hall welcomes the inquiry and says it will help prevent future miscarriages of justice. He's particularly pleased it's promising to look into police procedures.

"What they did to those eyewitness statements [in Alan's case] was despicable," he says.

"Where were the procedures then? Where were the layers of supervisors above the people that were doing this to say, 'Hey, no, stop'? None of that was in place back in the eighties."

No one should have to experience what his family - and the Easton family - went through, Hall says.

"What they do and what they find in this inquiry can help a long way to prevent wrongful convictions, like Alan's."

A matter of race

The inquiry will also examine other factors that can make witness identification evidence unreliable, including cross-racial identification.

Te Kāhui chief executive Parekawhia Mclean says some Māori people in particular have been wrongly identified as perpetrators by Pākehā.

"There is research and literature that has identified identification being different between different races," she says.

"We think that's particularly important here in a New Zealand context. It's tended to be less accurate, so we wanted to explore that more through this inquiry."

The commission is going into the inquiry with an "open mind", Mclean says.

However, she notes there is clearly room for improvement given the number of high-profile wrongful conviction cases - and the number of applications the commission has received - which includes problems with witness identification evidence.

Police say they are aware of the inquiry and will co-operate "as and when required".

"It would not be appropriate for police to comment further while the inquiry is underway," says a spokesperson.

-Soumya Bhamidipati/RNZ.