Police have re-opened an investigation into the unexplained death of a baby twin who died nearly four years ago from severe head injuries.
Karlos Stephens was just 10 months old when he died in Rotorua Hospital in November 2014 and the senior detective leading the inquiry says the explanation for his injuries was "vague".
The previously unreported cold case is similar to one of New Zealand's most infamous child abuse cases - the deaths of the Kahui twins in 2006 - in that a small number of adults were in the house with Karlos and his twin brother in the days leading to his suspicious death.
"We've never been totally happy with the version of events we've been given," said Detective Senior Sergeant Lindsay Pilbrow.
"We're confident certain people who had contact with Karlos on the weekend of his death know a lot more. Some are being very forthcoming and we appreciate that.
"But other members of his extended family, particularly those who were caring for him over the relevant time, have not been so forthcoming."
New medical opinions from experts in Scotland and Australia, reviewed by others in New Zealand, have given the investigation team more certainty the injuries suffered by Karlos were not accidental.
Pilbrow would not be drawn on the exact nature of the injuries - or what possibly caused them - other than to say Karlos suffered "significant" head injuries.
Karlos and his twin brother were living with extended family at the time of his death on November 30, 2014.
Those caregivers were not home on the days when the injuries were likely to have been inflicted and had been co-operative with police, Pilbrow said.
But the severe nature of Karlos' injuries did not match with the explanations given by the adults living in the house in the days leading up to his death, which Pilbrow described as vague.
"The explanation would be ... there's a lack of explanation," Pilbrow said.
"There's a lack of explanation from a small number of specific people who had care of these young children around the events of the weekend, the night before, and how this young baby could have received these injuries."
Pilbrow urged anyone with knowledge of what happened to talk to the police.
"We've never been totally happy with the version of events we've been given.
"Baby Karlos isn't here now to speak for himself. There are people who know what happened and they need to step forward."
The Bay of Plenty has one of the worst rates of child abuse in New Zealand and Pilbrow, who is the police district's manager for child protection, urged people to keep their eyes open.
"This is yet another case of a young child who has, on the face of it received significant injuries, which has led to his death," Pilbrow said.
"I think it's important people be very vigilant as to what's going on in family and friends' homes. To not be scared to step forward and ask those tough questions."
A number of high-profile child homicides happened even though family and friends were aware - or should have been aware - of the abuse.
This was the case in the murder of 3-year-old Nia Glassie, whose murder in 2007 horrified New Zealand.
"There needs to be a criminal sanction here and compulsory criminal reporting is a must," Coroner Wallace Bain wrote in his inquest findings.
The following year, the Crimes Act was changed to make it an offence for someone who lives with, or is "closely connected" to a child to fail to protect them from physical or sexual abuse.
Turning a blind eye, or closing ranks as a family, is now punishable by up to 10 years in prison.
However, just nine people have been prosecuted - with only seven convictions - since the law came into power five years ago, according to figures released under the Official Information Act.
And despite the national outcry after each death, New Zealand's rate of child abuse remains among the worst in the developed world.
The actual numbers of child homicides can vary, depending on source, as investigations into suspicious deaths can take months or even years to finalise.
But there have been 94 cases of child murder or manslaughter between Nia's death in 2007 and 2015 - slightly above the historic annual average of nine deaths - according to an official police document released in March last year.
• Anyone with information about the death of Karlos Stephens should call the Rotorua police station on 07) 349 9400