One of the brothers accused of killing Damilola Taylor thrust a broken beer bottle into the schoolboy's leg, the Old Bailey has heard.
Damilola bled to death in Peckham from a leg wound
Danny Preddie, 18, and his brother Rickie, 19, of Peckham in south London, are being tried for manslaughter for a second time - a charge they both deny.
Prosecutors described the attack in November 2000 as cruel and callous.
Neither brother chose to help, instead they left the 10-year-old bleeding in a stairwell in Peckham, the jury heard.
Victor Temple QC, prosecuting, said the brothers had a troubled background with little discipline or security at home.
At the time of the attack, they were aged 12 and 13. Danny was living in a local authority home in Bermondsey, south London, while Rickie was a day pupil at the Orchard Lodge Assessment Centre in Anerley, south London.
Mr Temple alleged the Preddies approached Damilola after an after-school computer club at the local library.
"One of the Preddie brothers had broken and/or had possession of a recently broken beer bottle - a fact that the other brother fully appreciated," he said.
He then alleged one of them had thrust the bottle into Damilola's thigh.
"Both the brothers were streetwise beyond their age, but neither chose to come to his aid, neither called for an ambulance or other assistance despite it being obvious to anyone that Damilola was in need of immediate medical attention."
Damilola was discovered by carpenter Bill Casal, who followed a trail of blood up the stairwell in Blakes Road.
While waiting for an ambulance, Mr Casal saw three youths standing in the road.
"One of them looked up towards Mr Casal and proceeded to make a gesture with his left hand across the thigh of his left leg," said Mr Temple.
Two days after the death, Rickie Preddie and two other youths were seen by police officers at the scene, which had by then been cleaned.
Earlier, the prosecution told the jury they had a compelling case against the brothers including evidence of blood and fibres found on their clothes and footwear.
A trainer shoe taken from Danny Preddie's room had a spot of Damilola's blood on it, and a fibre "indistinguishable" from his school trousers, the court heard.
It was also alleged fibres indistinguishable from those from Damilola's uniform were on his Danny Preddie's clothes, and one indistinguishable from his sweatshirt was found on the schoolboy's jacket, the court heard.
In Rickie Preddie's case, a drop of Damilola's blood was found in the cuff of a sweatshirt, alleged to have belonged to him.
At a trial earlier this year, the Preddies were cleared of murder and assault with intent to rob, but the jury failed to reach a verdict on the manslaughter charge.
The case was adjourned until Tuesday.