Liam Whoriskey, 25, of Glenabbey Gardens in Derry, denies murdering Kayden McGuinness who was left in his care.
Kayden was found dead in the child’s family home at Colmcille Court in the Bogside on September 17, 2017.
The trial opened at Derry Crown Court today, Wednesday, September 25, and is expected to last four weeks.
The BBC has reported that opening the prosecution case, Peter Irvine QC told the jury that the three-year old’s death was not immediate.
He said his injuries were as a result of repeated assaults.
On the night of September 16, 2017 Kayden’s mother Erin McLaughlin had stayed with friends overnight, Mr Irvine said.
She had left the three-year old boy and her five-month old daughter in the care of the accused, with whom she had been living for eight months.
Mr Irvine said Ms McLaughlin returned home the next morning after receiving a phone call about what had happened to her son.
On the morning of September 17 the defendant woke up just before 10 am and went into Kayden’s room, the prosecution said.
He found the child lying on his back with his face turned towards a wall.
The court was told Mr Whoriskey touched the child and the boy was cold and he could not locate a pulse.
The defendant called police from a neighbour’s flat.
The accused said to one of the PSNI officers, ‘how do I tell his mother?’, the court was told.
Mr Irvine said a post mortem examination found at least 15 bruises to Kayden’s scalp caused by “blunt force trauma” that resulted in swelling and bleeding to the brain.
The prosecutor said the child’s death was caused by the injuries.
One of Kayden’s left ribs had also been fractured, he said.
On the day before Kayden’s death, the court was told the defendant had taken him shopping in Derry city centre.
CCTV footage showed the defendant dragging Kayden by his hood and wrist, the court was told.
A shop assistant also heard the defendant acting in an aggressive manner towards Kayden and swearing at the boy.
In his first police interview, the accused told officers Kayden’s mother had squeezed Kayden’s chest, hit him hard and shaken him after he’d swallowed a 2 pence coin.
The court was told Whoriskey said during the shopping trip he had refused to buy the child a toy egg and that had caused him to throw a tantrum.
The accused told officers it was not uncommon for Kayden to injure himself during tantrums.
In a subsequent police interview on June 11, 2018, the defendant told officers Kayden was a hyperactive child who frequently hurt himself by running into a sofa or by jumping off the windowsill at home.
During a third interview the defendant accepted there were no injuries to Kayden when he put him to bed the night before the child was found dead.
Whoriskey is further charged, and denies, two counts of child cruelty on separate dates in August and September 2017.
The trial continues.