Cassius Turvey, a 15-year-old Noongar Yamatji boy, died 10 days after prosecutors say he was chased, knocked to the ground and "deliberately struck to the head" with a metal pole in Perth's eastern suburbs on October 13, 2022.
Emergency doctor William Begg treated Cassius at Midland Public Hospital in the hours after he was allegedly attacked.
He told the court Cassius had suffered multiple head injuries, including a five-centimetre laceration on his forehead.
"It penetrated all layers of the skin to expose the skull," Dr Begg told the West Australian Supreme Court on Wednesday.
"It was quite a clean laceration."
He also found a bruise near Cassius's temple and a "complex" wound that "penetrated the full thickness of (his) ear".
He observed that Cassius was asking the same questions repeatedly, prompting Dr Begg to order a CT scan of his head.
That found bleeding inside Cassius's brain and bleeding between his brain and his skull.
Aleesha Louise Gilmore, 23, her boyfriend Jack Steven James Brearley, 23, and his mates Brodie Lee Palmer, 29, and Mitchell Colin Forth, 26, are on trial, charged with murdering Cassius.
Prosecutors allege Brearley struck Cassius in the head twice with a metal shopping trolley pole while "hunting for kids" because somebody had smashed his car windows.
They allege Forth, Palmer and Gilmore helped him and knew his intent before the incident.
The jury heard paramedics took Cassius to the hospital after the alleged attack about 5.30pm and Dr Begg treated him about 9.30pm, a "brief time" after he was triaged.
Under cross-examination by Brearley's lawyer Simon Watters, Dr Begg said he was unaware of the delay.
Cassius was later transferred to Perth Children's Hospital and stayed there until October 18 when he was discharged.
He was re-admitted to the Midland hospital hours later about 2.30am on October 19.
Dr Eugene Henry said Cassius had suffered seizures and was "in a bad way".
A fresh CT scan revealed that the bleeding and pressure inside Cassius's brain had increased.
The teen was transferred back to Perth Children's Hospital about half an hour later.
Neurologist Snigdha Saha said "the injured side was now pushing against the opposite side".
"It was significant," she said.
Doctors operated on Cassius but he died four days later.
Forensic pathologist Leana Downs said Cassius's cause of death was complications of head injury.
She said there was evidence of increased cranial pressure, strokes, swelling of the brain and pneumonia.
The trial continues.
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