A paediatrician with expertise in child abuse says there is no way the fatal injuries suffered by the Kahui twins could have been sustained by accident.
The three-month-old brothers, Cru and Chris, died in 2006 from severe head injuries.
At their inquest on Monday, the panel of four medical experts provided a graphic list of head injuries.
They also said the boys had broken ribs that were at least two weeks old at the time of death.
Dr Patrick Kelly, who is one of the four medical experts giving evidence to the coroner, said the boys had definitely been victims of child abuse.
"There is no other medical explanation for this presentation other than traumatic brain injury. I can't conceive of an accidental mechanism that could have occurred in the circumstances in that household and be unknown to everyone present," he said.
Dr Kelly said normal handling of a baby could not result in the severity of injuries suffered.
Also at the inquest, a doctor from the United States, Carole Jenny, said parts of the boys' brains had extreme injuries.
She said both had suffered haemorrhaging in another part of the head that was consistent with a dangerous injury to the brain.
Dr Jenny also told the inquest the twins would have had a much better chance of survival if their father had taken them to hospital after he found one wasn't breathing.
Chris Kahui gave Cru CPR after finding him with blue lips. But the boys were not taken to hospital until the next day.
Dr Jenny said swift action could have made a difference.
The inquest resumed in Auckland on Monday after a seven-month adjournment.
The twins died after being admitted to Starship children's hospital in Auckland in June 2006. The boys' father, Chris Kahui, was acquitted of their murder following a High Court trial in 2008.