The fingerprints from the Crewe house and interior of their Hillman car are critical clues to these unsolved double homicides and clearly have the potential to confirm the identities of those in both locations in the period immediately following the crimes committed at Pukekawa on 17 June 1970.

There is no doubt in my mind that not only was there a murderer in the Crewe house, but that at least one other was involved in the feeding of, and caring for Rochelle Crewe, the sole survivor of these brutal executions. From the documented evidence now available, it is likely that this other person was in the Crewe car in the five days between the murders and the reporting of the disappearance of Jeanette and Harvey Crewe by her father, Len Demler, five days later.

There were a significant number of unidentified fingerprints in the Crewe house and a thumb print on the interior rear vision mirror of the murdered couple's car. The latter is especially relevant as two independent witnesses reported seeing an unknown woman driving the Crewe car the morning after the murders - four days before their disappearance was reported.

I do not accept the "presumption" by the Crewe inquiry fingerprint specialist, Mervyn Dedman, that these unidentified fingerprints all belonged to Harvey Crewe. As that Police officer himself reported, it had been impossible to take prints from the body of the late Harvey Crewe after his recovery following two months of immersion in the Waikato River. On that basis, and on the clear evidence pertaining to at least one other person being involved in the aftermath of these crimes, it is my clear view that not nearly enough work was done during the original murders investigation in 1970, nor in the decades that have followed, to establish the identity of those unidentified prints.. Presumptions are not evidence in my view and I am surprised that any trial judge would allow a Police witness, on oath, to make such claims.

I have also been advised that the photographic images of the fingerprints, including several dozen which remain unidentified - as in not proven to belong to any particular person - are now missing from the Crewe homicide file.

If that is indeed the case, then questions must be asked as to when that event occurred, who had control of the homicide file when that occurred and how is it that absolutely crucial exhibits should disappear while in the custody of New Zealand's state law enforcement agency. If key exhibits from what is undoubtedly the most scrutinised double homicide case cannot be kept safe while in the custody of the New Zealand Police then answers must be demanded and explanations given at the highest levels.

From my perspective, having researched the Crewe murders and the Police investigation for 39 years, there can be no innocent explanation for this disappearance. A cynic may be excused for believing that this is another act by a member, or members, of the New Zealand Police aimed at preventing the resolution of this most famous of cold cases. In the process of ensuring that these fingerprints are no longer available for examination, whoever was responsible for the destruction of these exhibits has also probably denied Rochelle Crewe the ultimate justice she has been seeking for her deceased parents.

In 1973, the late Detective Sergeant Stan Keith, on the instructions of his boss at that time, Detective Inspector Bruce Hutton, dumped a swag of key exhibits at the Whitford tip, including the cartridge case used to fabricate a case against Arthur Thomas. When the then-Justice Minister Martyn Finlay learned of those acts by the Police he said they had left him desolate and deeply disturbed. This latest act - which must clearly be seen as having been perpetrated with sinister intent - similarly has left me deeply disturbed.

Chris Birt is a researcher and writer on the unsolved Crewe murders.