Private investigators reviewing Scott Guy's murder say debate over whether there was a significant police failure in the hunt for the killer can be resolved for about $100,000.
The four-man team wants two effluent ponds on Guy's Manawatu farm emptied, saying there is a chance they hide key evidence - the murder weapon, a dive boot which was a key in Ewen Macdonald's trial, or the remains of puppies missing from the time of the crime.
They say grain sacks missing from the farm may have been used to dispose of evidence and could have been weighted to sink into the sludge.
Police drained the ponds but did not dredge the sludge.
Police say the draining was sufficient, but Scott's widow Kylee Guy joined the mounting pressure for action. "They've got to do it," she said.
It's been six months since private investigator Mike Crawford and his team were asked by Kylee and the Sensible Sentencing Trust to find out who killed her husband.
Macdonald was acquitted of Scott Guy's murder last year.
Crawford told the Herald on Sunday sludge in the two ponds could hold the key to the case.
"I can't think for the life of me why they weren't drained, then completely emptied out," he said.
Crawford said he was told police were reluctant to properly search the ponds as they believed evidence could be destroyed as it was pulled up through suction machinery.
But Crawford said a South Island dredging company had told him that was "complete rubbish".
"You put grilles and nets and stuff over the end so nothing actually gets sucked into the machine," Crawford said. "I don't want to be openly critical but it's something the police need to address. There is a metre of sludge on the bottom of those ponds which has not been searched."
Crawford said Kylee told him: "The police have got to do it."
Forensic scientist Dr Nicholas Powell told the Herald on Sunday he had done similar investigations.
Skeletal remains of the puppies would not have survived but grain sacks which may have held them would.
He said a dive boot and a gun or ammunition would probably still be intact. Dredging Solutions managing director Rob Grant said the 10-day search and recovery would cost about $100,000.
But police Superintendent Sue Schwalger, national manager of professional standards, said further work on the ponds was not warranted as they had been drained.
"Police have been advised that any item of interest would be captured within the equipment used to drain the ponds and would need to be physically removed by the contractor. The contractor has advised police that no such items have been caught in the equipment."
Crawford said it now came down to money. Aside from a small amount of money to cover airfares, he and his team had not been paid for the 200 hours he estimated they had put into the case.
"There are other areas to look at but it means going down there and spending time."
The initial investigation had been pro bono, but to test their theories, it would cost.
"Unfortunately, funding has become an issue. If funding was available, we could give this inquiry substantial momentum." Kylee Guy's family, the Bullocks, hoped donors might help.
"The Bullock family will never rest until they have justice for Scotty. We are so thankful for all that the New Zealand police and investigators have done and continue doing," a statement said.
"Should people wish to help us fund the investigation, please contact us at firstname.lastname@example.org."
The parents of Macdonald, who is serving time for other offences, yesterday supported calls to keep the inquiry alive in an effort to find out the truth.