The family of Arthur Allan Thomas are accusing the police of harassment and bias in their review of the Crewe murder.
Mr Thomas was twice convicted of the murders of Jeanette and Harvey Crewe, who were shot at their farm in Pukekawa in 1970, before being pardoned in 1979.
He was paid $1 million in compensation for the time he spent in prison.
The couple's daughter, Rochelle, asked police to re-investigate the killings, but instead they are reviewing their original investigation.
Arthur Allan Thomas' brother-in-law, Buster Stuckey, says two detectives arrived unannounced on his doorstep earlier this month asking if he had an alibi for the night of the murders.
He says it's clear the police are still trying to pin the crime on Mr Thomas, who was also re-interviewed this month.
Mr Stuckey says his wife and Mr Thomas's two brothers were also spoken to by police.
Both Mr Stuckey and one of Mr Thomas's brothers, Desmond, say it's clear the review of the Crewe murders is biased and independent experts should take over.
Police say the questioning was professional and it would be remiss not to speak to people connected with the case.
AAP reports Rochelle Crewe has been kept informed of progress. She was aged 18 months when her parents were killed.
She was looked after by an unidentified woman for five days before the killings were discovered.
AAP reports the review covers 90,000 pages of documents. It is being independently assessed by a senior barrister.