A teenager stabbed to death outside an Oxford Street store in London on Boxing Day died of a "single stab wound to the heart," a post-mortem has found.
Horrified shoppers saw the 18-year-old, named as Seydou Diarrassouba from Mitcham, stabbed to death in broad daylight during a fight at a Foot Locker sports shoe store. Just hours later another youth was stabbed in the leg on the same busy street.
Formal identification by family members is yet to take place but the Metropolitan Police said they were "satisfied" the victim was Diarrassouba.
The teenager was described as a "good kid with a big personality" by school friend Munawar Shaikh, 20, who also named the victim from south London.
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 cut up about it," the Press Association quoted him as saying.
Shaikh added it was more likely to be a "misunderstanding between youths" than gang-related violence.
A Facebook page called R.I.P. Seydou was set up for friends to pay tribute to the dead teenager, who was also known by the nickname "Nutz".
One message, posted by Okoko Felly, read: "my heart gose to ur mum and dad bruv, whats your big sis an ali gonna do with out u, man why dose life ave to be lyk dis. forever in our hearts nutz i luv u boi. only 18"
Justin Osei wrote: "R.I.P man its not gonna be the same not seeing you around you were almost like a monument to mitcham, sad times".
Eleven people are being held in custody at several London police stations following the incident, including five 19-year-olds, three 17-year-olds, two 22-year-olds and one 16-year-old. Police said a number of weapons had also been recovered from the crime scene.
Three men were also arrested in connection with the second stabbing, which happened near Oxford Circus underground station at about 6.20pm.
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 Diarrassouba.
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.
But Scotland Yard issued a statement denying a taser was "deployed" during the chaotic scenes.
Commander Steve Rodhouse said the Met's Diplomatic Protection Group "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.
"Officers can be seen in the footage pushing the crowd back and one officer is shown to remove his Taser from its holster, although at no time was it ever deployed.
Police have appealed for witnesses with mobile phone footage of the stabbing to come forward.
Speaking outside Scotland Yard, Detective Superintendent John Sweeney said: "There were several people who witnessed this event, both inside and outside the store.
"A number of them recorded it on camera phones, and we're particularly interested in those people coming forward so we have access to that footage.
"But also anyone else who saw what took place inside and outside the store, we want them to come forward and assist us in establishing exactly what took place."
He urged witnesses to contact police at the incident room on 020 8721 4906 or Crimestoppers on 0800 555 111.