Police are considering whether to lay criminal charges against Chris Kahui for not taking his twins to hospital the night one of them stopped breathing.
Cru Kahui stopped breathing on the evening of June 12, 2006, and had to be revived with CPR.
The three-month-old infant was described by witnesses as pale, with rolling eyes and purple lips.
Three adults in the house wanted to call an ambulance or take the twins to hospital, but Chris Kahui resisted.
The babies were not taken to hospital until the next day and died from brain injuries five days later.
Four medical experts now agree the Kahui twins might have survived if they received medical treatment earlier.
A report written by Dr Carole Jenny, an American paediatrician who specialises in child abuse, and released to the Herald said the twins "could possibly have been saved".
She sat on a panel of medical experts at the inquest alongside Dr Patrick Kelly of Starship Hospital, Professor Roger Byard and Dr Terence Donald, who was a witness for the defence at the murder trial of Chris Kahui.
According to the findings of coroner Garry Evans, all four experts unanimously accepted that Cru "could well have been saved" if he had been taken to hospital after he stopped breathing.
"If Chris' fatal injury was received at the same time as Cru's injury, the sooner he received care (as with Cru) the better the outcome would have been," said Mr Evans.
This evidence was not given at the 2008 trial of Chris Kahui. The Herald understands the police are now investigating whether charges can be laid against him for not taking the twins to hospital earlier.
The officer in charge of the police investigation, John Tims, has been promoted to superintendent and is now the district commander for Counties Manukau.
Last night, Mr Tims said the police thoroughly investigated the deaths of the Kahui twins and put all available evidence before the courts for examination and judgment.
"Police are still considering the evidence heard in the inquest and will not make any further comment until that analysis is completed."