Aaron John McLeod is alleged to have caused a catastrophic brain injury to the two-year-old son of his then-partner in May 2022 at her house in Coffs Harbour, on the NSW mid-north coast.
Neither the child nor his mother can be identified for legal reasons.
The 40-year-old was accused on the first day of his trial in the NSW Supreme Court of going into the boy's room and inflicting injuries, including fracturing his pelvis and ribs, while the boy's mother was asleep in the house.
Crown prosecutor Ben Allison said in his opening address the boy's injuries could not be explained by a series of accidents in the preceding 24 hours.
The toddler fell down a set of slippery steps and banged his head in the afternoon before he died, the jury was told on Monday.
In the hours before the Crown alleges McLeod fatally injured him, the boy was also found banging his head against a cupboard in his bedroom, Mr Allison said.
But medical evidence suggested neither of these incidents were serious enough to cause the injuries the boy was later found to have sustained, he said.
"It wasn't uncommon for (the boy) to bang his head during the night ... (it) is not an uncommon behaviour in toddlers," Mr Allison said.
"These injuries (the fractures and brain injury) … are unusual and require significant force to be inflicted."
Mr Allison conceded the prosecution case was circumstantial and said there would be no witnesses who would testify seeing McLeod inflict any injuries on the toddler.
But he told the jury McLeod had expressed his frustration about the child's behaviour multiple times to others despite having only met his mother two months earlier.
McLeod allegedly said the boy was "an out of control c*** who needs to be sorted out", the jury was told.
Police allegedly found a blood-stained T-shirt with the victim's blood in the washing machine when they searched the house the day he died, the jury heard.
The boy's mother also later allegedly discovered a pillowcase with her son's blood in a wardrobe, Mr Allison said.
McLeod has denied causing the boy's death and his barrister is expected to say there is no evidence linking him to the boy's injuries.
The trial continues.
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