Police in London have a special unit to probe this type of crime but believe they have only scratched the surface

Witchcraft-based abuse first came to national consciousness with the murder 12 years ago of Victoria Climbi? by her guardians. After her death it emerged that the police and other authorities had missed several opportunities to step in and save the eight-year-old. Her death led to a public inquiry and produced major changes in child protection policies in England.

Since Climbi?'s murder, agencies have learned a great deal more about the ritualised abuse and torture of children. But figures collated by the Metropolitan police merely scratch the surface, detectives believe, of a hidden crime that is still under-reported.

In the past 10 years police in greater London have investigated 83 incidents of child abuse and torture linked to witchcraft and other religious rituals. Of these children, four ? including Kristy Bamu ? were murdered during ritualised violence. One police source said more cases of this kind were coming to light ? either because the problem was increasing or because the light shone on the issue had led to increased reporting of incidents.

The horrific cases of child abuse are often familial and often emerge from within the African diaspora. While most of the child killings have led to perpetrators being brought to justice, others remain mysteries.

One of those murdered was "Adam", a boy aged between four and eight whose torso was found in the Thames in 2001. His killers have never been found and, after lengthy inquiries, detectives are convinced he was killed in some kind of religious ritual.

In 2005, four years after Adam's body was found, two women and a man were convicted of child cruelty for torturing and threatening to kill an orphaned refugee who they claimed was a witch.

Known as Child B to protect her identity, the young Angolan girl was cut with a knife, beaten with a belt and shoe and had chilli peppers rubbed in her eyes to drive the devil out of her. The eight-year-old was also sealed in a laundry bag and told she would be thrown away into a river.

The child, who had been brought to Britain in 2002 after her parents were killed in Angola, was found shivering in her bare feet on the steps outside a council flat in Hackney, east London, where she suffered her ordeal. She later told police that she had been surviving on tea and bread.

Ritualised abuse involves witchcraft-style exorcisms within many different cultures, including Caribbean, Congolese and Asian communities, according to the Met.

The police set up Project Violet seven years ago to target the problem and work with other agencies to raise awareness of children at risk.

But detectives know that Kristy Bamu will not be the last child to suffer this kind of torture and abuse.

"We know this is an under-reported crime, we know this is a hidden crime," said Det Supt Terry Sharpe, head of Scotland Yard's child abuse investigation command.

"That is why Project Violet is working with communities to try to raise the awareness within the community and among professionals so people can see the danger signs."

The task is challenging. Only a few days before Kristy Bamu's murder another young child lost her life as a result of ritualised abuse. The four-year-old girl was found stabbed to death in the kitchen of her east London home a few days before Christmas 2010. Her heart and other organs had been cut out and strewn around the flat and her mother, Shayma Ali, was found chanting by her daughter's body. Ali later pleaded guilty to manslaughter on the grounds of diminished responsibility.