Mr Lovelock said the original homicide investigation was being analysed by modern police tools to provide a definitive assessment of the evidence gathered.
The assessment was a painstaking and time-consuming process looking at material from a range of sources, including paperwork from the 1971 and 1973 High Court trials which led to Arthur Allan Thomas being convicted twice.
Mr Thomas was pardoned in 1979 after nine years in jail and a 1980 royal commission concluded 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.
Mr Lovelock said all paper documents have been copied into an electronic database that provides integrity to the review and is essential in managing 90,000 pages of material.
"Every document is being read and pertinent material extracted for analysis," said Mr Lovelock. "Any new or additional information passed to police will be evaluated and considered in the context of the review."
Ms Crewe told the Weekend Herald that police had replied to her letters twice to say the review would take "a matter of months", without stating a deadline.
"While I appreciated that this process would take a while, I do feel that I have been very patient - letting them get on with the job at hand.
"However, my original fear was that without an independent body overseeing the process, the whole process would lack accountability and credibility.
"To date this proves true, because it seems that they can take as long as they like to do the review, and without someone independent there pushing it along or setting target dates, doesn't make the police accountable to anyone but themselves."
Mr Key had earlier refused Ms Crewe's plea to appoint an independent body to investigate, rather than a police review of the case, which she believed was tainted by corruption.
Last October, she said the failure of the police to reopen the case when Mr Thomas was pardoned had led to years of speculation, 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."
The 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 farmhouse. He also found Rochelle crying in her cot.
Doctors who examined her said she could not have been abandoned for five days since the murders, so someone must have fed her.
Witnesses reported seeing a blonde woman at the house who was never identified.
Anyone with information should call Detective Superintendent Andy Lovelock on (09) 529-5658 or Crimestoppers anonymously on 0800-555-111.
