He emerged holding the infant saying he had stopped breathing. The baby's lips were blue and his eyes were rolled back into his head.
Boynton had called an ambulance but did not say how he came to be in that condition or that he had stopped breathing.
"The ambulance assessed the child and considered no further treatment was necessary, he misled the ambulance officers and they went away thinking it was an over-anxious parent dealing with a choking fit," Justice Toogood said.
However, during the night and following morning the baby had ongoing seizures and the ambulance was again called where he was first taken to Whakatane Hospital before being transferred to Starship Hospital in Auckland.
The child suffered serious brain injury with bleeding around the brain and behind his eyes. The hospital also found evidence of a previous inflicted injury.
"Based on expert evidence the injuries were likely caused through shaking or other violent act like throwing him on a bed."
The child, who has permanent name suppression, is now 3 but is still suffering from the injuries.
"He struggles to move his left side of his body and his left foot. He is behind his peers in learning and the future is uncertain whether he requires further surgery. He could never be a normal child or a normal adult for that matter," Justice Toogood said.
"As a father of nine children you are an experienced caregiver ... he was in every sense of the word vulnerable, defenceless and dependent on you."
Some of Boynton's children were in the court gallery when he was sentenced. They yelled out, 'bye Dad, love you Dad,' as he was led to the cells.
His prison term is to be served on top of the 15 month prison sentence he is currently serving for assault on the boy's mother.
