The independent body set up to look into serious miscarriages of justice has referred its first case back to the courts, two years after it was established.
The Criminal Cases Review Commission (CCRC), also known as Te Kāhui Tātari Ture, said a 15-year-old, referred to only as Mr G, was sentenced in 2001 to 11 months in an adult prison. He was charged with assault, drink-driving and unlawfully getting into a motor vehicle.
Sentencing laws at the time prohibited anyone under 16 from being imprisoned unless the offences were indictable, meaning they were serious enough to require a jury trial - but Mr G's offences were not.
However, district court documents filed at the time had the wrong date of birth, indicating Mr G was 17 instead of 15.
While Mr G appealed his sentence - saying the judge failed to recognise his personal mitigating features, including his age - his appeal was dismissed and the High Court hearing proceeded on the basis that he was 17.
Mr G asked the commission to review his convictions and sentence in September 2020. It then gathered evidence from government agencies showing he was only 15 in 2001.
CCRC Chief Commissioner Colin Carruthers KC said the case illustrated why the commission was set up.
"Mr G was only 15 years old when he was sentenced to imprisonment, contrary to the law which prohibits the imprisonment of those under 16 years of age," he said.
"A mistake had been made and went undetected. It was this mistake which led the commission to the decision that it was in the interests of justice to refer the case to an appeal court so that the issue could be considered and, if appropriate, the convictions quashed."
The case also showed that miscarriages of justice could happen across the whole range of criminal offences, Carruthers said.
"The cases which tend to attract the most public attention are those involving high-profile and serious crimes, such as murder with long periods of imprisonment," he said.
"As a result, miscarriages of justice involving lesser crimes often get little or no attention.
"However, the consequences are similar: the stigma of a conviction, separation from family, the difficulty of reintegration into society, and sometimes the brutal treatment in prison."