Arthur Allan Thomas' brother carried out his own forensic tests to discredit the evidence that convicted his brother.
This week, Ray Thomas has revealed he planted shell cases in the Crewe garden - replicating the actions of detectives investigating the case. He proved buried shell cases would discolour compared with the shiny case presented to the court.
Arthur Allan Thomas was twice convicted over the deaths of Harvey and Jeannette Crewe in 1970, and then pardoned. A Royal Commission of Inquiry found a shell case from Thomas' gun had been planted in the Crewe garden by police officers.
The killings left baby Rochelle, 18 months, abandoned in her cot. Now in her 40s, she has asked police to review the case.
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The Thomas family spoke out this week about detectives Bruce Hutton and Len Johnston after Deputy Commissioner Mike Bush told mourners at Hutton's funeral that Hutton had "integrity beyond reproach".
Ray Thomas said the shell cases had been found in the garden four months and 10 days after the murders, but he knew they couldn't have been in the ground that long.
"In June 1971, my middle brother, Richie, Bob Hills, Dad and I went to the Crewe property and planted shell cases under the cover of darkness.
"On our return after about four months and 10 days we retrieved the shell cases and I had them photographed and sent to Wellington. We did another lot in June 1999 ... both lots look very different to the exhibit."
Ray Thomas and his brothers believe another Pukekawa man is the killer.
"He had the only other rifle in the district and that's where the axle that was found with the bodies was last seen. He also had a motive. He cut the wrong hay paddock in the 1970 summer. Harvey Crewe would not pay him. He wasn't fingerprinted and his rifle was not excluded."
The police review of the original investigation is nearing completion.