A South Australian man, already in jail after shaking his baby so hard the boy was left severely brain-damaged, will be sentenced for a second time after the death of the child.
Brandon Lee Harris on Thursday pleaded guilty in the Supreme Court to the manslaughter of the boy who was just six weeks old at the time of the incident in May, 2018.
He is already serving a four-year jail term after admitting to recklessly causing harm.
The court heard that the young boy had lived for just 16 months with a raft of serious health issues including blindness, feeding difficulties and breathing problems.
He couldn't roll over, sit up, crawl or stand and was not able to move his arms and legs.
In a victim impact statement read to the court, the boy's mother told how she was shocked when she first learned it was his father who was responsible for the injuries.
"I remember being stunned, it felt like someone had punched me in my stomach," she said.
She said her "heart was broken" when she later lost custody of her son, and she was devastated when told the boy had died.
"I lost my mind. I remember physically punched walls and screaming, crying, sobbing.
"I will forever miss my beautiful baby boy."
Defence counsel Chris Weir said Harris accepted that he would spend longer in jail than his original term but urged the court not to impose a crushing sentence.
He said Harris had been struggling to deal with what he had done and with the death of his son.
Mr Weir said prior to the "horrendous event" Harris had been a good father even though he had little in the way of parenting skills.
"It is something he will live with for the rest of his life."
On the day of the offending, the boy had been unsettled and Harris, who was not coping with the situation, had just "snapped", his counsel said.
Prosecutor Lucy Boord said while legislation required any new non-parole period for Harris be four-fifths of the head sentence, the crown accepted that there were special circumstances, in this case, to allow for a shorter term.
Harris will be sentenced at a later date.