Spots of blood and fibres link three youths to the killing of schoolboy Damilola Taylor, the Old Bailey heard.
Ten-year-old Damilola was stabbed on his way home from school
Forensic evidence missed during the first investigation was discovered after four other youths were cleared of the 10-year-old's murder, jurors heard.
A drop of Damilola's blood was found on a trainer and sweatshirt, proving the three attacked him, say prosecutors.
Hassan Jihad, 20, of Peckham, south London, and two brothers, aged 17 and 18, deny murder and manslaughter.
They also face charges of assault with intent to rob.
Damilola was stabbed in the thigh with a broken bottle in Blakes Road, Peckham on 27 November 2000, say prosecutors.
The court heard he was walking home when he was attacked by youths who wanted to rob him.
"The Crown say that Damilola Taylor was not prepared to be robbed, he stood his ground," said Mr Temple.
"In consequence, the three defendants resorted to the level of violence they anticipated would occur if they met with resistance, namely the use of the bottle to cause really serious bodily harm."
Damilola's parents were in court to hear the killing described as a "callous and brutal" attack.
He managed to make his way to a stairwell and up a couple of flights of steps before collapsing and bleeding to death, the court heard.
Damilola was found by carpenter Guillermo Casal, who had noticed a blood trail on the pavement.
Damilola's parents Richard and Gloria sat at the back of the court
As he waited for an ambulance to arrive, Mr Casal noticed three black youths standing in the road, the court heard.
"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 later, the youth, who the prosecution claim was the older brother, had allegedly returned to the stairwell as police stood guard.
Two officers knew him and noticed he was "not his usual self" but quiet and subdued.
The court heard that the 17-year-old, then 12, lived in a local authority care home while his brother, then aged 13, was a day pupil at an assessment centre which he failed to attend on the day Damilola was killed.
Prosecutor Victor Temple told the jury Mr Jihad, then aged 14, admitted being in Blakes Road that day.
He said there were no witnesses to the attack or to place the three on Blakes Road immediately before the attack, but "powerful circumstantial evidence" gave a clear picture of events.
Four youths aged under 18 were cleared of killing Damilola in 2002, after which Mr Temple said all the evidence was re-examined and new forensic evidence was found.
"The totality of evidence now available points with certainty to the criminal involvement of these three defendants and demonstrates their participation in the fatal assault," he said.
The trial continues.