A fresh allegation of potential evidence tampering has emerged in the Crewe murder case - but this time it is not against the police.
The bullet which supporters of Arthur Allan Thomas claimed identifies another suspect in the 1970 murders of Jeannette and Harvey Crewe may have been "substituted" while secured in the national archives, according to a police review of the case.
Archives New Zealand and Des Thomas, brother of Arthur, say he was closely supervised when examining the exhibit in 2004 and could not have switched any evidence.
Police have said since 1970 that a rifle belonging to Arthur Thomas is consistent with the murder weapon as the fatal bullets were marked by six lands and grooves - the marks left on the projectile as it leaves the barrel.
A firearm belonging to another Pukekawa farmer, John Eyre, was not eliminated as the murder weapon during the original police investigation but was after further testing during the 1980 Royal Commission of Inquiry.
The Eyre rifle bullets were shown to have five lands and grooves - not six.
Des Thomas was unable to convince police to investigate Mr Eyre and visited Archives New Zealand in 2004 with a forensic scientist to examine Exhibit 209 - a .22 bullet test-fired during the royal commission.
The bullet examined by the pair did have six lands and grooves - consistent with the murder weapon - which was later corroborated by ESR testing in 2006.
But after the discovery, the Eyre rifle was again retested by ballistics experts and the bullets again showed five lands and grooves.
The Crewe Review team, led by Detective Superintendent Andy Lovelock, noted five bullets were fired through the Eyre rifle in 1980 and one was labelled as Exhibit 209 for the royal commission. The bullet held in the National Archives as Exhibit 209 "inexplicably differs considerably in appearance" when compared with the other four, according to the Crewe report.
The bullet in question was embossed with the number "8" on the base of the projectile, while the bullets used to test the Eyre and Thomas rifles in 1980 were not.
"The review team have consulted with Archives New Zealand. Their records are not conclusive as to who had access to this exhibit whilst it has been in their custody. Records confirm the identity of only two people that had been afforded access," says the police report. "The only conclusion that can be drawn ... is that at some point Exhibit 209 has been substituted with another bullet or mislabelled."
Mr Eyre was categorically ruled out as a suspect by the Crewe Review this week. Des Thomas said any suggestion he had switched the bullets was "bullshit" and the inclusion of the possibility in the report was inaccurate and unfair. "Archives were asked about this later on and they said it was wrapped up in the original packaging from the royal commission. The archivist was present at all times. I didn't go by myself - I'd have been silly to go there by myself. I took a forensic expert."
Mr Thomas said the initial inquiries from his lawyer to arrange the visit resulted in Archives New Zealand making it clear there would be a set of eyes on anyone visiting at all times. "We can't just go down there and grab exhibits and do what we like."
A spokesman for Archives NZ said staff "felt strongly" that Exhibit 209 was not substituted or mislabelled while in its custody. "Everyone who has access to evidence is supervised closely at all times."
If the bullet was mislabelled, he said it was more likely to have occurred during the royal commission.
Mr Thomas also alleged the police had swapped the barrel on the Eyre rifle some time between 1970 and 2006, although ballistics experts used in the Crewe Review said there was no evidence to support this.
The police had too easily dismissed the barrel theory evidence, said Mr Thomas. "They've taken everything out of the evidence we have given them and manipulated it to suit whatever case they had."