The teenage boy being held after a 15-year-old girl was stabbed to death in south London was known to local community groups, according to a charity worker who works to combat youth violence.

The girl, who has not been named, was stabbed in the neck with a foot-long knife while on her way to private school during Wednesday morning rush hour in Croydon, a witness said.

A 17-year-old boy, who knew the victim, was arrested just over an hour after the attack which took place on busy Wellesley Road at around 8.30am.

Witnesses have said the girl and her alleged attacker were not in a relationship.

Anthony King, chairman of My Ends – a project helping combat youth violence in Croydon, said the boy had been known to local community groups for the past couple of years.

Mr King was with the girl’s family after the incident and said they were “heartbroken”.

He added: “She had a bright future ahead of her. She was in her GCSE year.”

Mr King described the girl as an “absolutely incredible young lady” and told of how others said she was “jovial, very comedic”.

Meanwhile, a steady flow of well-wishers left flowers and cards near the scene on Wednesday evening.

One of the cards left near to where the attack took place read: “Sorry we live in this crazy world this makes no sense.

“Fly high up there my mummy will look after you. RIP beautiful, forever young, taken too soon.

“Thoughts and prayers are with your family and friends, God bless.”

Another said: “Rest in peace little princess. So sad your life is taken away at your prime you have touched my soul.”

Emergency services were called to Wellesley Road at around 8.30am but the girl was pronounced dead at the scene 50 minutes later.

‘The blood was coming like water’

A bus driver and a passer-by were seen desperately trying to save the girl before emergency services arrived, with police at the scene within two minutes.

The suspect was arrested within 75 minutes of the stabbing in nearby New Addington.

Victor Asare, 50, told how he saw a boy stab the girl in the neck with a knife which was “black, thin and about a foot long”.

“The boy wore a black blazer, the girl wore green. It looked like the girl didn’t want the boy to come closer,” said the security worker. “The blood was coming like water.”

He said the boy ran away and “everybody was crying and screaming”, adding: “The girl was on the floor.

“We tried to catch him and a lot of people tried to save the girl. I was so shocked, I was shaken. It’s somebody’s daughter.”

‘Is my friend dead?’

Michael Fyffe, a passer-by, told Sky News he was on his way to work when he saw a “commotion” and was told a girl had been stabbed.

He said: “There were loads of people who had just come off the bus and then I think two of the girl’s friends came out and they were trying to rush over towards the body.

“So myself and a few of the other people tried to hold her back and just say, ‘Look let them try and help your friend’, and she was just screaming, ‘Is my friend dead? She’s my best friend’.”

A mother of two, who wanted to be named only as Bridget, said: “I was on the bus before and came off and walked back down, I saw them resuscitating her.

“The driver was holding her, and a lady. The emergency services were already here when I walked back.”

She said two other schoolgirls, believed to be the victim’s friends, were trying to get through the police cordon but were held back.

A red double decker bus on route 60, three police vehicles and about a dozen officers, as well as a forensics tent, could be seen in the taped off area outside the Whitgift Centre.

Chief Superintendent Andy Brittain said at a news conference from the scene: “This is every parent’s worst nightmare.

“I know the officers who responded this morning, along with our emergency service colleagues, are devastated at the victim’s death. This is an emotion I share, and I know people across Croydon will be feeling the same.”

Girl’s family ‘devastated’

James Watkins, from Mainz World, which runs prevention and intervention projects for children and young people, said he was supporting the girl’s “devastated” family, who arrived on the scene between 9am and 10am.

“They were devastated and I would say more importantly in shock, I don’t think it feels real for them,” he said.

The Old Palace of John Whitgift School, which the girl attended, has said in a statement: “We are deeply shocked by the senseless and tragic death of our much-loved and valued friend and pupil.

“It will take some time for the Old Palace community to come to terms with this terrible news, and we will offer support to our pupils as we try to do so.

“Above all, we send our love and deepest sympathies to the girl’s family at this unimaginably distressing time.”

‘Impossible to comprehend’

Mayor of London Sadiq Khan said he was “absolutely heartbroken” by the death.

“My thoughts and prayers are with this young girl’s family and friends, and the whole community, at this unimaginably awful time,” he said

Met Police Commissioner Sir Mark Rowley said: “The senseless murder of a 15-year-old girl on her way to school is impossible to comprehend.

“It was moving and humbling to meet many members of the exceptional Croydon community who have come together in support of a family now dealing with the most unimaginable grief.”