"Such injuries can only be caused by the application of significant force, such as a violent shaking and or striking the infant's head against a hard surface," the police summary of facts stated.
Later that day, Sisley took Baby A to his partner and told her he was not breathing and having seizures. Medical assistance was sought and the baby was flown to Auckland's Starship Hospital. He was later discharged into the care of Child, Youth and Family.
Victim impact statements were submitted to the court by the child's carer and pediatrician who was helping with the boy's rehabilitation.
"The victim is nearly two and settled in his new environment however he is also recovering to some extent from his physical injuries," Justice Graham Lang said.
"There is signs of weakness down the left side of his body and it's unknown whether this is likely to be permanent."
It was also unknown how severe and permanent the baby's brain damage was.
"Your offending will have at least some impact [on the baby] for the [remainder] of his life,'' Justice Lang told Sisley.