A promising teenage footballer described as a "role model" for his community may have been murdered in a fight over a girl.
Junior Nkwelle, 15, was stabbed to death outside a block of flats and one theory was he may have been attacked by a jealous boyfriend.
He was pronounced dead at the scene and police said the killing was not believed to be gang-related.
A 14-year-old girl has been arrested on suspicion of murder.
Solomon Smith, 27, a youth support worker at Marcus Lipton Youth Centre a few yards from the scene, said: "He was one of our locals, and had been coming here for about two years.
"He was a very good footballer. When he came in, he always played football indoors here.
"He was a very quiet guy, you wouldn't think anything like this would happen to him.
"When we left here at 8pm last night, we heard a lot of commotion outside. The youngsters are saying that Junior might have been trying to flirt with a girl, who said 'my boyfriend's from Peckham and he's coming down', there was a fight and Junior was stabbed.
"From about 9.30pm I was getting told that he'd died.
"Because it's Brixton, and there's blocks of flats, you get gang troubles round here. There's been gang wars with guys from Stockwell and Tulse Hill, and that's what we are trying to tackle."
Faith Marriott, 30, who lives locally, looked at the flowers, and said: "I empathise with his mum. He used to coach my son at football. So what does that say about him, that he's only 14, and wants to coach little ones.
"He was a friendly boy, he wasn't in a gang.
"When children die, people don't believe he could be innocent. We mums would like to be better off and live in a better place, but we try.
"I hope CCTV cameras were working. My little brother Adrian was shot dead near here eight years ago and nobody has been convicted of his murder."
Her friend Dawn Pusey, 45, a mother of five, said: "It's sad that the youths are thinking about killing each other instead of their education."
Mrs Marriott's brother David, who helps run local youth project Lambeth Tigers, said: "He's been coming to us for about four months and coached younger boys at football. He was a brilliant kid, only 15, but a good role model for this community. He was always smiling, an asset - to lose somebody like this is devastating."
An incident room was opened under Detective Chief Inspector Charles King, who said the murder is not believed to be gang-related.
He added: "We would appeal for anyone who has any information or witnesses to come forward as soon as possible."
Anyone who could assist the inquiry was urged to call detectives on 020 8721 4054 or Crimestoppers anonymously on 0800 555 111.