On the day of the incident neighbours reported hearing screams that somebody was on fire after a large cloud of black smoke was seen rising from the back yard.
Police arrived at the scene to find the ground scorched and Ms Whatarau badly burnt from the waist up, smelling strongly of petrol.
Mr Haraki was hosing her down and also had burns to his face, neck and arms and appeared to be going into a state of shock.
The pair were both taken to the Hawke's Bay Hospital where Mr Haraki was then transferred to Lower Hutt Hospital and Ms Whatarau to Middlemore Hospital in Auckland where she died; having suffered burns to 52 per cent of her body.
Released more than four years after her death, yesterday's inquiry enables her family to obtain a final death certificate.
However there was insufficient evidence in both the determination of who poured the petrol over the woman and who ignited the petrol, Coroner Devonport said.
"With key witnesses refusing to make statements to enable the facts to be established, and with there being right of those witnesses to decline to answer questions and give evidence at an inquest, at this state there is insufficient evidence to determine whether Ms Whatarau died as a result of suicide, unintentionally by her actions, or as a result of actions of another party."
Detective Sergeant Mark Moorhouse asked any members of the public with information about the incident to contact police.
"There are people who were present at Amelia's home when she received her fatal burns that have the ability to provide details of what occurred and the Police still would like to formally interview them before being in a position to make any decision on the circumstances that contributed to Amelia's tragic death on that day."
Section 97 of the Coroners Act 2006 outlines the Solicitor-General or the High Court may order another inquiry to be opened if, among other listed reasons, new facts are discovered.