The Independent Police Conduct Authority has found multiple shortcomings in a police investigation of an intermediate school teacher, and police misconduct in a subsequent teachers' disciplinary hearing.
The authority said there were deficiencies in a 2014 police investigation of an innappropriate relationship between teacher Samuel Back and Reiha McLelland, 13, who died later that year. Her death was the subject of a coroner's hearing.
The investigation was conducted by an officer whose superior, Officer A, was the chairperson of the board of trustees at Mr Back's school, Gisborne Intermediate.
The authority said Officer A's conflict of interest was not properly managed which meant the investigation was not adequately supervised.
"The investigation plan was inadequate and not all appropriate enquiries were conducted; information obtained from the interviews of Reiha and Mr Back was not recorded appropriately; and the interview of Mr Back was not conducted properly," the authority said.
The authority said officer A was not actively involved in the investigation, its outcome was not pre-determined, and there was not enough evidence to lay charges against Mr Back.
However, when the case came before the Teacher's Disciplinary Tribunal in 2016, Officer A signed a letter from the school asking for name suppression in order to protect any future inquiries.
The authority said that was patently wrong and misleading, contrary to police policy and amounted to serious misconduct.
"If the supervisor had intended to mislead the Teachers Council, he would have been guilty of the offence of attempting to pervert the course of justice. However, such an intent cannot be proved", said the authority's chairperson, Judge Colin Doherty.
The Teachers' Disciplinary Tribunal found Mr Back and his wife Angela Mepham guilty of serious misconduct in February 2016. It deregistered Mr Back, then aged 42, and censured Miss Mepham, then aged 33.
Mr Back had taught the girl while she was in Year 8 at Gisborne Intermediate School in 2013 and began an intense relationship with her after she ran away from home and stayed overnight with the couple in October that year.
The tribunal said he had breached the most elementary obligation owed by teachers to students - to do everything in his power to ensure the safety of his student.
Police said they accepted the findings, and noted that while the IPCA agreed with police there was insufficient evidence to charge the teacher with a criminal offence, it also found the investigation to be deficient in several respects.
"In particular, it is crucial that all officers - no matter what rank they are - are able to identify a potential conflict of interest and know how to appropriately manage it," Eastern District Commander Superintendent Tania Kura said in a statement.
"Eastern District Police have conducted an internal review of the investigation and our findings were broadly in line with the IPCA's findings."
Superintendent Kura said Officer A resigned in April last year, cutting short an employment process that had been underway at the time.
She said police had introduced training in order to ensure conflicts of interest were better handled.
Gisborne Intermediate confirmed today the former police officer was still the chairperson of its board of trustees, but he would be stepping down.
Meanwhile, a lawyer acting for the family of Reiha McLelland, Moira Macnab, told RNZ News the family was exhausted by the inquiries related to their daughter's case.
"They've done it to try and improve things for others," she said.
"They're not doing this to get back at people, they're doing it for positive change."
Ms Macnab said the family hoped to meet with police next year to discuss changes they had made to their processes.
She said they remained worried that Mr Back could apply to work with children without declaring that he had been struck off the teachers' register because of an inappropriate relationship with their daughter.
They wanted a law change making it mandatory for children's organisations to check for disciplinary information with any registration authorities or professional bodies to which job applicants had previously belonged, she said.