UN special rapporteur Juan Mendez says Australia still has questions to answer over its failure to protect witnesses to the alleged murder of Reza Barati.
Mr Mendez told the ABC he had still not received a response from the federal government six months after he tabled a report into the alleged torture of witness, Kurdish asylum seeker Benham Satah, and another Iranian man.
He said Australia should have done more to protect the men.
"I think it's never too late for Australia to do what it should have done some time ago," Mr Mendez told the ABC.
"Providing witness protection is something that should have been done on a timely basis, but it can still be done and I'm hoping that the Australian government will decide to do so."
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Mr Satah told the ABC's AM program PNG guards intimidated him daily, despite promises from Papua New Guinean authorities he would be protected.
"They want me dead," he told AM.
Mr Mendez's March 5 report to the UN General Assemly alleged the two men were tortured on Manus Island and threatened with rape unless they withdrew their statements.
Two Papua New Guinea locals are facing court in relation to Mr Barati's death.
Mr Barati died from a head wound sustained during a riot on Manus Island in February, 2014.
