When Stokes Valley parents Giselle Whaanga and Nathan Weston put their identical twins Ariana Karlota and Tiare Tipani to sleep, they wrapped each baby in her own blanket, put two thin blankets on top to keep them warm and laid them on their backs in their shared cot.
The girls hadbeen born to the couple after three miscarriages since the birth of their first daughter.
On July 16, 2001, Ms Whaanga fed them and gave them a dose of Pamol for a mild fever.
For the first time, the parents put the babies' heads on a pillow. The twins fell asleep about 10.30pm. The next morning, Ms Whaanga awoke to discover the three-month-old girls dead in their cot.
Almost three years on, experts cannot agree on the cause of their death. At an inquest in Wellington yesterday, perinatal pathologist Jane Zuccollo said there was no evidence of infection.
The twins' clothing had been very damp, which was unusual, their mother said. Dr Zuccollo said that and the amount of bedding - a fleece layer on top of the mattress, covered by a sheet and several blankets - might suggest hyperthermia as babies were not well equipped to deal with excessive heat, but that could not be proved.
Pillows were not recommended for infants because they could block a baby's airway.
However, forensic scientist Jim Sprott said a British laboratory's analysis of the cot mattress and bedding found antimony and phosphorous.
The theory was that the elements, with fungi, generated toxic gases that interfered with a baby's nervous system, leading to cot death.
Chemical pathologist Michael Crooke said the mattress was not tested for fungi and there was no medical evidence that the gases would affect the nervous system as Dr Sprott claimed.
Wellington coroner Garry Evans was critical of a lack of thorough investigation into sudden and unexplained infant deaths in the past, though he praised the police investigation in the twins' case.
He thanked Ms Whaanga and Mr Weston for attending the hearing, adding: "Their little ones were cared for in the most beautiful way."
