The Old Bailey trial of seven teenagers accused of the murder a 15-year-old boy at Victoria station ground to a halt today after jurors were discharged.
A new jury is to be sworn in and the case, concerning the death of Sofyen Belamouadden in March last year, will begin again next week.
Judge Christopher Moss said he had taken the decision after legal submissions.
Samuel Roberts, of Camberwell, Obi Nwokeh, of Bermondsey, and Enoch Amoah, of Camberwell, all aged 18, deny murder.
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 the charges.
Yesterday it was decided that an eighth defendant, 18-year-old Victoria Osoteku, of Deptford, south London, would be tried separately from the seven involved in the current proceedings.
A total of 20 are accused of Sofyen's murder in March last year, with further trials due to take place later this year.