A teenager attacked in the Boxing Day sales on London's busiest street died from a single stab wound to the heart, his post-mortem has confirmed.
Horrified shoppers saw the 18-year-old stabbed to death in broad daylight during a fight at a Foot Locker sports shoe store on Oxford Street.
Just hours later another youth was stabbed in the leg on the same busy street.
School friend Munawar Shaikh (20) said the dead man was Seydou Diarrassouba who lived on Phipps Bridge Road in Mitcham, south London. The pair went to Rutlish High School in Merton, south London, together and grew up in the same area.
Mr Shaikh, who now studies broadcast journalism at Leeds University, said: "I heard about it on social network sites. It's devastating. I had lost contact with Seydou but he was such a big personality and a person everyone in Mitcham would know.
"He was just a good kid who always had a smile on his face. I have not had a chance to go out yet but I imagine everybody will be upset about it."
Asked if he thought the killing may have been gang-related, Mr Shaikh said: "I cannot say if it was a gang thing, it seems more like it was just a misunderstanding between youths."
Amateur video footage posted on YouTube showed angry scenes outside the Foot Locker store as police held back remonstrating youths while paramedics attempted to revive the stabbing victim.
The video appears to show a policeman using a Taser electroshock weapon on one of the youngsters, who can be seen exchanging shoves with officers.
However, Scotland Yard later issued a statement denying a Taser was "deployed" during the chaotic scenes which followed Mr Diarrassouba's murder. Commander Steve Rodhouse said: "One of the first units to come across the incident were officers from the Met's Diplomatic Protection Group who were driving past.
"On arrival they were confronted by certain elements of the crowd who were extremely agitated and officers had to protect the victim and those administering emergency first aid to him."
Police have appealed for witnesses with mobile phone footage of the stabbing to come forward.
"R.I.P Seydou, just the other day I was talking to you. Known from when we were little, wish you perfect peace in paradise. Gone but never forgotten hun. Will always remember our lil dancing moments in primary school and you always giving me joke. Sleep tight hunny".