Violent force which might not be heard outside the room where it was used was almost certainly used to fatally injure the Kahui twins, a child abuse specialist has told a jury in Auckland.
The injuries were of a type experts in New Zealand had never seen in 20 years, Starship Hospital paediatrician Patrick Kelly said.
Dr Kelly was giving evidence at the trial in the High Court in Auckland of 23-year-old Chris Kahui, who is accused of murdering his three-month-old twins Cru and Chris.
The premature twins were admitted to hospital on June 12, 2006 and died of brain trauma five days later.
The Crown says Kahui was the only person who could have inflicted the fatal injuries. Kahui's lawyers say somebody else, probably the twins' mother Macsyna King, inflicted the injuries.
Dr Kelly, who sees a lot of children who are possible victims of abuse or neglect, was out of the country when the twins died but was subsequently asked by police to give an opinion on why the babies died.
He said both babies had four types of injuries to their brains, two of which were extremely unusual.
Baby Chris Kahui also had a diabetes condition which meant his kidneys were unable to retain water which Dr Kelly thought was caused by an injury to his brain, along with brain bruises, torn nerve fibres in the middle of his brain, and some bleeding between his skull and brain.
Dr Kelly said the injuries to both were "very severe, right at the top end of the scale" and could only have been caused by "violent deceleration of the head".
In Chris' case the external injuries suggested he most likely hit a hard or thinly padded hard surface with very little give in it.
External injuries were not apparent on Cru so there was more chance he was slammed against a soft surface, though Dr Kelly said he could not be sure.
"The important thing is the deceleration. You could cause these injuries in a few seconds," he said.
"I think in both twins it is force that I would describe as violent. By that I mean force that any objective third party coming into the room and seeing it being applied would say `stop that, you're going to hurt that baby'."
Despite this, he said if the door was closed when the children were hurt it was unlikely anyone outside would have heard the injuries, Dr Kelly said.
He said the contusional tears -- tearing injuries to parts of the front of the brain -- were extremely unusual. A British study of 53 child deaths found such tears in only four, all under the age of five months.
Dr Kelly said Dr Beth Synek, an Auckland-based specialist who gave evidence at the trial last week, "said she's been looking for them for 20 years and this is the first time she's found them".
The prosecution case is expected to finish tomorrow.
