Three happy slap thugs forced two terrified teens to punch each other while they filmed it on a mobile phone.
They forced the two teens into a Croydon alleyway before taking their jewellery and other possessions.
David Noakes, 20, and his two young girl accomplices insisted the terrified pair kneel facing each other then ordered them to punch each other to win back' their property.
The victims were told by their tormentors that each blow landed would result in one of their possessions being handed back.
The horrendous robbery was only uncovered when the girl's - who cannot be named - headteacher confiscated a mobile phone from her which contained footage of the attack.
He contacted the police and detectives traced it back to the attack on Croydon Crown Court today ordered the 15-year-old girl back to juvenile court for sentencing.
David Noakes is facing jail.
He is expected back in court in December following psychiatric reports.
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