An ordinary 14-year-old who turned into a killer

She appeared to be an ordinary 14-year-old girl experiencing the growing pains of adolescence who did little to draw attention to herself on the grim south London estate she frequented.

Known as a likeable tomboy, she played football with the boys, excelled in French lessons and wrote long passages in her diary about her intense crush on a 19-year-old lad in the neighbourhood.

Yet one Friday night in October last year, a couple of weeks before her 15th birthday, she was to become a central figure in one of the most shocking crimes of recent times, which led to the sadistic killing of a stranger.

David Morley, 38, a barman sitting on a bench along the South Bank, central London, was beaten to death in a perverse gang killing, in which the teenage girl, who cannot be identified for legal reasons, kicked his head "like a football" and filmed the savage attack on her mobile phone.

Rejected by her alcoholic mother at the age of seven, she spent a lonely, ruptured childhood shunting between relatives' homes until she was taken into foster care in May last year.

Her unravelling appears to have been triggered by her friendship with a group of older male youths on the Ethelred housing estate in Kennington, south London, which began a year before the death of Mr Morley. The sudden transformation was noticed by neighbours who said she would look "spaced out", appeared to be smoking cannabis and was increasingly scruffy in appearance.

The posse of four youths were this week convicted of Mr Morley's manslaughter and face a lengthy jail sentence. They were described at the Old Bailey as inflicting random violence on strangers for thrills, triggered by code words and recorded on mobile phones to replay for their pleasure.

When the aunt with whom she was staying on the estate in Kennington fell seriously ill last May, she had been put into a foster home in South Norwood, despite attempts by social services to keep her in her family circle.

The months leading up to the killing in October were settled, according to an independent review by Barnet social services. She was doing better at school, was not in trouble with the police and showed no signs of criminal aggression, although she was occasionally rude to teachers at her school in south London and complained of the tedium of lessons in her diary.

She played football with local boys every Saturday near St Thomas' Hospital, and was one of the few white girls who had bridged the divide between the black and white communities on the estate. Yet those who knew her felt something was wrong.

A resident said: "She would go into the youth centre on the estate, where mostly black children go. She'd pop her head round the door, buy sweets and talk to Reece Sargeant (another convicted gang member). She was always polite. But then suddenly, I would say hello to her and she wouldn't answer back. It was if she hadn't heard me. She looked completely spaced out."

She developed a crush on Barry Lee, an older boy who was acquitted at the Old Bailey, writing of him fondly in her diary and drawing love hearts by his name, but her feelings remained unrequited.

A source said her first serious boyfriend was a black 17-year-old gang member on the estate who often initiated the violence in their "happy slap" sprees by punching strangers in the face. She spoke in a "south London Caribbean" accent to mimic the boys and was keen to fit in, according to Mr Hamlyn.

At one point, her foster parents asked social workers what to do if she asked to spend the night out at a friend's house, which suggests that she may have been doing "all-niters" by this stage, in which the gang went on sprees of violent attacks overnight.

Her appearances at court in the past year have been largely unaccompanied by family members. Her sister was still in Ireland, her mother is said still to have addiction problems, and her foster family, who were "incredibly distressed" by the news, have distanced themselves from her to protect their two children.

On the day of the crime, she changed out of her school uniform, took the bus from South Norwood back to her aunt's flat on the estate and went on a "happy slap" spree that would change her life forever. In the early hours of Saturday morning, she sat and drank Panda Pops at Lee's home and then ambled home.

Little did she know that on her 15th birthday, she would be making the first of her many appearances at the Old Bailey.