Rochelle Crewe says she will not give up her quest to bring to justice the killer of her parents.
The only child of Harvey and Jeannette Crewe has angrily rejected Prime Minister John Key's refusal to launch an independent inquiry into the unsolved murders of her parents in 1970.
Last year, Ms Crewe was disappointed when the police decided to review - rather than reopen - the investigation of the murders.
Ms Crewe then wrote to Mr Key to formally ask that an independent body investigate New Zealand's best-known cold case and suggested that an overseas judge be in charge.
The Prime Minister refused and said any new investigation of the case rested with the police.
"As a Minister of the Crown, I cannot direct them to reopen the case," Mr Key wrote.
However, Ms Crewe has written back to Mr Key to say she is offended by his response and "will not let this matter rest".
She was aware the Prime Minister could not interfere with the day-to-day running of the police - and pointed out that she did not ask him to.
"In fact that is the furthest thing from my desire as I would like someone completely independent of the police, possibly an overseas judge, to oversee the investigation and therefore enforce some accountability on the police," Ms Crewe wrote.
"What I did ask was for you to reopen the case and I thought it was self-evident that you would recognise that an independent inquiry was needed in order to achieve this."
She said that former Prime Minister Robert Muldoon had ordered a royal commission of inquiry after Arthur Allan Thomas was pardoned for the Crewe murders in 1979. Justice Robert Taylor, Australian head of the 1980 commission, said it was "an unspeakable outrage" that Detective Inspector Bruce Hutton and Detective Len Johnston buried a shellcase from Mr Thomas' rifle in the Crewes' garden to link him to the crime.
But Paul Neazor, QC, the Solicitor-General at the time, decided against charging the pair because he believed there was not enough evidence to justify a prosecution.
"Mr Muldoon did not 'interfere' with the Police Commissioner of the day, as you suggest I am asking you to do, but he did introduce an independent arbiter to review what was clearly a miscarriage of justice," said Ms Crewe.
"There is clear evidence today that there continues to be a miscarriage of justice. Certainly no justice for my parents' murders has been delivered by not allowing the case to be reopened after the pardon of Thomas."
Rochelle Crewe was 18 months old when found crying in her cot five days after her parents were last seen alive.
"A terrible bloody mess" was what Len Demler, Jeannette Crewe's father, found in the couple's farmhouse in Pukekawa, south of Auckland, in June 1970.
The body of Mrs Crewe, 30, was recovered from the Waikato River in August 1970, her jaw badly broken. Her 28-year-old husband was found in the river a month later, weighed down by an axle. Both had been shot.
After three months, the police were under huge pressure to solve the crime, and quickly found two pieces of evidence to implicate Mr Thomas, who lived on a farm 13km from the Crewes.
Axle stubs hidden on his farm tip apparently matched the axle that weighed down Harvey Crewe. Then police found in the Crewes' garden the case of a shell fired from his .22 rifle - despite having found nothing there a few months before.
Mr Thomas was convicted of the murders and spent nearly 10 years in prison. He was pardoned in 1979 after mounting public protest.
But Rochelle Crewe said it was unacceptable that the case was never reopened.
"Is it right that all the injustice throughout this case just gets swept under the carpet and no one is ever held accountable?" she wrote to the Prime Minister.