Hopes that high technology could solve the 30 year-old Crewe murders have been dashed - meaning the killer may never be known.
Bruce Hutton, the former Detective Inspector who led the murder investigation, believes forensic science techniques not available in 1970 could now be used in a renewed inquiry.
He's urging policeto take up the controversial case again to seek vital clues establishing once and for all from which rifle the fatal bullets were fired.
"I am keen to see the bullet fragments taken from the Crewes' bodies examined under computer enhancement methods.
"It would show which rifle it came from. We collected all the rifles in the district. We test-fired them and the DSIR [the then Department of Scientific and Industrial Research] kept the evidence."
He believes the late Dr Donald Nelson, the DSIR scientist who delved deeply into the murder evidence, put the telltale bullets in a safe place where they can still be found.
But Scientists at Auckland's Institute of Environmental Science and Research Ltd ( DSIR's successor) believe bullets and fragments taken from the Crewes' bodies no longer exist and photographs of ballistic evidence could not be enhanced sufficiently to strengthen the case.
Kevan Walsh, a forensic scientist specialising in firearms examination, said he had grave doubts about the value of the many police photographs still on hand.
"The bottom line is that looking at photographs is no replacement for looking at that seen under a microscope at the time. No amount of enhancement will get around it."
He agreed that advances in DNA profile analysis and crime scene examination might have assisted the police inquiry had they been available three decades ago. But there was too little evidence now on hand.
"A particular rifle cannot be identified as being the one that definitely fired a bullet from an examination of only the fired bullet.
"It is necessary for a comparison of this bullet to be made with a bullet test-fired in the rifle.
"Without obtaining and test-firing the offender's rifle, such identification cannot be made."
