A 15-year-old schoolboy was killed in a "merciless" knife attack, planned on Facebook, during rush hour at London's Victoria station, the Old Bailey heard.
Sofyen Belamouadden was chased by an armed group of 20 teenagers before being stabbed, punched and kicked.
The GCSE student, from Acton, west London, died on 25 March 2010.
Victoria Osoteku, of Deptford, Enoch Amoah, of Camberwell, Obi Nwokeh, of Bermondsey, and Samuel Roberts, of Camberwell, all aged 18, deny murder.
'Knives from Argos'
They have also pleaded not guilty to conspiracy to cause grievous bodily harm and violent disorder.
Four 17-year-old youths, two from Streatham, one from Stockwell and one from Brixton, also deny each of the charges.
Details of the trial are now able to be published for the first time after reporting restrictions were lifted.
Sofyen was killed after tensions between pupils from two west London schools, some of whom saw the station as "home territory", jurors heard.
Mark Heywood QC, prosecuting, said the attack on the schoolboy took place in "broad daylight" in front of hundreds of commuters.
Sofyen was confronted by a group with a sword at Victoria station.
He was then chased into the Tube station before being stabbed nine times, including to the lung and chest.
CCTV footage was shown to jurors of him being set upon and left lying on the floor.
"He was given no chance of life," said Mr Heywood.
On the day of the attack, two of the defendants were said to have left school to buy a £3.99 block of knives from Argos, Mr Heywood said.
Witnesses saw youths at the station with weapons including a samurai sword with a blade 20-30cm long (9-12in), a Swiss Army knife and possibly machetes and screwdrivers, the court heard.
"So brazen and confident were his killers that they openly carried the various weapons that they used with them as they ran towards him and together hunted him down," Mr Heywood added.
Trial to resume
The attack on the schoolboy was in revenge for an "inconsequential" skirmish over a girl at Victoria station the previous day when a boy from a rival school had been left with a bloody nose, the court heard.
During chats on mobile phones and social networking site Facebook that evening, some of Sofyen's alleged killers discussed getting weapons including a samurai sword the next day, jurors were told.
A total of 20 teenagers have been charged with with Sofyen's murder, conspiracy to cause grievous bodily harm and violent disorder.
For practical reasons, all 20 are not being tried at the same time.
The trial, which was not sitting on Tuesday, will resume on Wednesday.