Four people, one of them a teenage girl, who attacked strangers at random and filmed some of their victims, have been convicted of killing a barman.
Case and Sargeant were among those convicted of manslaughter
David Morley's head was "kicked like a football" as the gang carried out their attacks in October 2004.
Reece Sargeant, 21, Darren Case, 18, a youth, aged 17, and the girl, aged 15, were convicted at the Old Bailey.
Eight people were beaten and stamped on in five incidents carried out for "pleasure", the court was told.
Barry Lee, 20, and a 17-year-old were cleared of all charges.
The random spree of violence, some of which was seen being filmed on mobile phones, was triggered by codewords, and involved kicking, beating and stamping on victims.
Bar manager Mr Morley had survived the Soho nail bombing
The four found guilty of manslaughter were cleared of murdering Mr Morley, a gay barman who had survived the Soho nail bomb attacks in 1999.
Prosecutor Richard Horwell said the gang, all from Kennington, south London, had planned to use violence "for what can only have been pleasure".
Mr Morley, whose nickname was Sinders, was sitting on a bench on the South Bank with his friend Alastair Whiteside in the early hours of 30 October.
Mr Whiteside said they were approached by the gang, who gave a brief acknowledgement before launching the sudden attack.
He described being attacked by a "smiling or laughing" man who "seemed to be getting enjoyment" out of the attack.
The girl, then aged 14, who cannot named for legal reasons, had kicked Mr Morley's head like a football as he lay on the ground, the court heard.
"The violence took the form of beatings, kicks and stamping. Weapons were not carried and were hardly necessary when you had such an advantage in numbers," Mr Horwell told the court.
Police investigating the killing said CCTV footage showed a female apparently filming the attack, but no evidence of photos or footage was ever found.
It has led to the case being described as a "happy slapping" killing - but Mr Morley's father Jeff is angered by use of the term.
He told BBC London: "It makes me angry that it's described as happy slapping because that makes it sound as if it was something not very serious, what actually happened to David was a lot more than slapping."
Case, Sargeant, the girl and the 17-year-old were remanded in custody for pre-sentence reports and will be sentenced on January 23.
They were also convicted of conspiracy to cause grievous bodily harm.