Mr Thomas was convicted in two trials - in 1971 and 1973 - of the 1970 murder of Harvey and Jeannette Crewe at their Pukekawa home, near Auckland. He was pardoned nine years later.
Thomas will today make a rare public appearance following the eulogy by Deputy Police Commissioner Mike Bush, who told mourners last week that the officer in charge of the Crewe murder investigation, Bruce Hutton, had "integrity beyond reproach".
Mr Hutton died before an independent review into the case and an investigation into police malpractice had been completed.
Speaking ahead of Mr Thomas' appearance today, his brother Des Thomas said Arthur was very angry.
"He is, because it shows that everything that the commission has said has been overlooked by the New Zealand police," he told Newstalk ZB.
"At the moment, we've got a so-called independent review getting carried out by the New Zealand police, and here we have the hierarchy backing up Bruce Hutton."
Des Thomas said he had been told that the police commissioner would also have attended the funeral had he been able to.
He said police manufactured evidence against his brother, which was protecting the guilty party.
"We just get frustrated, because all that we want is the truth. We just want justice at the end of the day. And the police won't move on from trying to make it look as though Arthur was involved in this case."
