Rochelle Crewe fears a police refusal to open a new inquiry into the unsolved murder of her parents, Jeannette and Harvey, 40 years ago is no more than a "continuation of police seeking to avoid the truth".

Speaking exclusively to the Herald, Ms Crewe said she feared the police were trying to protect their image.

Deputy Commissioner Rob Pope announced yesterday that the police would not reopen the case, but would instead conduct a "thorough analysis and assessment of the Crewe homicide file in an endeavour to answer questions raised by Rochelle Crewe".

But last night, Ms Crewe told the Herald the police response to her request for a new homicide investigation was disheartening, and the only "fair and honest" approach was to have the case reopened.

"I feel it is not adequate enough to just review what has already been done as this may not be a wide enough net to capture what was previously left out of the original investigation, as well as a failure to examine all evidence that was available to them at the time," Ms Crewe said.

"I am very disappointed, and I fear this is no more than a continuation of police seeking to avoid the truth and protect their image."

Ms Crewe said she was grateful for all the public support since she broke her silence in the Herald last week.

She said the failure of the police to reopen the case in 1979 when Arthur Allan Thomas was pardoned of the murders led to years of speculation, which was an "unnecessary injustice to my family".

"Had the police reopened the case after the pardon, perhaps they might have established who did this terrible thing to my mother and father.

"Perhaps now, with witnesses dead and evidence destroyed by the police, there is not sufficient amount to prosecute, but I do not accept that this was the case in 1979. These past events erode my confidence in the police and the justice system."

Mr Pope said police had spoken to Ms Crewe some weeks ago and "understandably she has questions that she wants answers to".

"We will do our very best, taking into account the limitation of time and the availability and recollection of witnesses."

Mr Pope said Detective Superintendent Andy Lovelock, the top investigator in the Auckland region, had been appointed to lead a "detailed analysis of all information available and acquaint himself with all the details".

He emphasised this was not a reopening or reinvestigation of the case, which was "one of the most scrutinised in New Zealand history" after two court cases, a royal commission and the subject of several books.

Mr Pope urged anyone with information to speak to the police.

Public support for a fresh inquiry has grown since Ms Crewe came forward for the first time since the 1970 killings.

She was just 18 months old when found crying in her cot in Pukekawa, south of Auckland, five days after her parents were last seen alive.

Mr Thomas - who spent nine years in jail before being pardoned - supported a new inquiry, as did his ex-wife, Vivien Harrison.

Labour leader Phil Goff backed a new investigation, as did Police Association president Greg O'Connor and Order of NZ members such as Sir Brian Lochore, Sir Paul Reeves and Dame Cath Tizard.

The unsolved homicide is one of New Zealand's greatest murder mysteries.

"A terrible bloody mess" was what Len Demler, Jeannette Crewe's father, found in the family's farmhouse in June 1970. He also found Rochelle crying in her cot.

Doctors who examined her said she could not have been abandoned for five full days since the murders, so someone must have fed her. Witnesses reported seeing a blonde at the house, but she was never identified.

The case gripped the nation for months. Mr Thomas' pardon resulted from years of protest from a retrial committee and other supporters and the personal intervention of the Prime Minister at the time, Rob Muldoon.

The royal commission set up to investigate the case found that Detective Inspector Bruce Hutton and Detective Len Johnston had planted a shell case in a garden at the Crewe house to frame Mr Thomas.

Rochelle Crewe was critical of the decision of the Solicitor-General in the 1980s, Paul Neazor, QC, not to lay charges against the two detectives because he believed there was not enough evidence to justify a prosecution.

"For some bizarre reason, the royal commission inquiry finding did not amount to a strong enough basis to prosecute these perpetrators," said Ms Crewe.

"On the flip side, it was enough of a finding to have a man pardoned."

*Detective Superintendent

Andy Lovelock is an experienced investigator with oversight of high-profile cases in the Auckland region, most recently the murder of Carmen Thomas.

He also reviews police inquiries and was critical of the so-called "Pumpkin" case in 2007, where An An Liu was found in the boot of her killer husband's car several days after she went missing.

Mr Lovelock also investigated how news media outlets obtained copies of top-secret police documents dubbed the "Terror Files" - evidence gathered before the raids on a group initially suspected to be terrorists in the Ureweras in 2007.

He has also investigated allegations against other police officers and mysterious disappearances or deaths.