It was the body of a five-year-old African boy. The corpse had no head. The legs had been severed above the knee and the arms cut off at the shoulder. All that remained was a torso dressed - grotesquely - in a pair of orange shorts, which had been thrown into the Thames shortly before it was discovered in September 2001. Death had been from a violent trauma to the neck, and the limbs had been "skilfully" removed after death by an experienced butcher.
Yet it was not the gruesome details of the murder and dismemberment that last week - almost two years later - led 200 police officers to launch nine simultaneous dawn raids across London and arrest 21 people. It was the contents of the stomach of the child, whom the police - in an attempt to restore some humanity to the desecrated body - had named Adam. That, and the orange shorts in which the post-mortem showed he had been dressed after death.
Ironically, the clue that first put them on the trail to the arrests turned out to be a false lead. The body had been found by Tower Bridge. Initially, detectives wondered if the mutilation might be an attempt to disguise the identity of the victim of an accident, a family row or a sex crime. But then, two miles upstream in Chelsea, they found the remnants of an African ritual, with a Nigerian name written on a sheet, carved into seven half-burned candles. Might this be a ritual killing?
In the event, the Chelsea paraphernalia turned out to be unrelated. But before the police discovered that, they had sent to Johannesburg for Professor Hendrik Scholtz, a South African pathologist who is an expert in so-called muti killings - in which adherents of traditional African magic take human body parts and grind them down to make potions they believe bring good fortune to those who drink them. The professor came to England and, after a second post-mortem, confirmed the detectives' fears. Muti had come to Britain.
The boy's throat, he confirmed, had been cut and his blood drained from his body, probably for use in some ritual. Most significantly his first vertebra - the one between neck and spine - had been removed. This is known in Africa as the Atlas bone, for it is said to be the bone on which the mythical giant Atlas carried the world. In muti it is believed to be the centre of the body, where all nerve and blood vessels meet, and where all power is concentrated.
There was something else. Adam's body was well-nourished and showed no signs of abuse, sexual or otherwise. Analysis of his stomach contents showed someone troubled to give him Pholcodine, a cough linctus, not long before he died. It was the classic muti scenario of an otherwise well-treated child being "volunteered" for sacrifice by his own family.
The police set out on two main lines of inquiry. The shorts - orange, they discovered, was a lucky colour in muti - carried the label Kids & Co, the brand-name for Woolworths in Germany. Detectives traced them to a batch of 820 pairs in size 116cm (age 5-7) that had been sold in 320 German stores. But then the trail went cold.
So, too, did a five-month trawl of London's ethnic communities. Detectives came across plenty of rumours that muti ceremonies were taking place, but no evidence - and no sign of an identity for the murdered child. Painstaking checks of the attendance registers of 3,000 nurseries and primary schools found no missing five-year-old who tallied with what was known of Adam. When they sent forensic evidence to the United States for testing it came back with the verdict from the FBI that the case was "practically insoluble". Even a public appeal by Nelson Mandela, broadcast across Africa, was fruitless.
But the dead child had not fallen totally silent. His DNA spoke up, as did the mineral levels in his bones. Analysts were able to establish that Adam had spent his life in a 100-mile corridor in the south-west of Nigeria, between Ibadan and Benin City. Revealingly, most of those arrested last week come from Benin.
The contents of his stomach were eloquent too. Forensic examination showed that the boy had been fed a muti potion of mixed bone, clay and gold.
There was something else. Analysis of pollen found in the boy's stomach showed he had been alive when he came to London. It is thought he was brought across Northern Europe, possibly via Germany, and lived in Britain for a few weeks before his murder. "We've uncovered what we believe is a criminal network concentrating on people trafficking," said Detective Inspector Will O'Reilly, who is leading the Adam inquiry. "We don't know how many children are involved in this operation, but it's certainly in the hundreds, if not the thousands, coming from mainland Africa through Europe into the UK."
Lurid accounts of child trafficking have suggested the trade is primarily to provide recruits for the sex industry. But police believe that the majority of trafficked children are put to work 12 hours a day, seven days a week, 365 days a year, in what amounts to a modern form of slavery. Only a tiny number fall victim to muti.
Much of muti is innocent. The term derives from umu thi, the Zulu word for tree, which has become a byword for any traditional medicine, good or bad. Its everyday form consists of potions made from Africa's indigenous herbs and plants to cure common ailments. It works. A pharmaceutical company has just signed a deal with the African National Healers Association to package some muti recipes. The South African Council for Scientific and Industrial Research has, with the aid of traditional healers, launched a "bio-prospecting" project to unlock the secrets of the nation's 23,000 indigenous plants.
Most adherents stop with the plant recipes. But some believe that more complex complaints can be cured with animal parts such as crocodile fat, hawk wings, monkey heads or dried puff adders. Before the last World Cup qualifiers a hippo, lion, elephant and hyena were slaughtered to make a potion for the Swaziland team to give its footballers extra strength.
Muti becomes disturbing when it is extended to the notion that human body parts can be used to heal or bestow special powers. For muti is not just a medicine, it is a metaphysic. It asserts that there is only so much luck in the world and each person has a limited supply of it. Very young children have not yet used all their luck, which can be transferred to whoever takes the medicine derived from their remains. This is the origin of the widespread African myth that sex with a virgin can cure someone of Aids: the younger the girl, the more potent the "medicine".
It is unclear how widespread human muti is in West Africa. But in South Africa, where the government set up a Commission of Inquiry into Witchcraft Violence and Ritual Murders after a spate of killings of boys aged between one and six in Soweto, it is estimated that at least 300 people have been murdered for their body parts in the past decade. The figure could be as high as 500 a year.
The killings are rarely impulsive. They are done to order by sangomas, or witch doctors, commissioned by clients with a particular need. Thus human skulls are placed in the foundations of new buildings to bring good luck to the business. Body parts are buried on farms to secure big harvests, severed hands built into shop entrances to encourage customers. Human hands burnt to ash and mixed into a paste are seen as a cure for strokes. Blood "boosts" vitality; brains, political power and business success. Genitals, breasts and placentas are used for infertility and good luck, with the genitalia of young boys and virgin girls being especially highly prized. There is a belief that body parts taken from live victims are rendered more potent by their screams.
Discovering all this provided the police with another clue. The genitals of the torso in the Thames had not been removed, suggesting that his killers needed muti potions for some other purpose. Adam had been sacrificed for non-sexual reasons.
It was almost a year after the discovery of Adam's body that the next piece of the jigsaw fell into place. A representative of the social services department in Glasgow contacted Scotland Yard and reported that one of their clients, a West African woman, had said she wanted to perform a ritual with her children. Her name was Joyce Osagiede. When police travelled to Scotland to arrest her they discovered among her daughter's clothes a pair of orange shorts of the exact size and brand as had been found on Adam. They also discovered that she had been living in Germany - the only place the shorts had been on sale - before coming to Britain with her children. It was not enough to charge her. She later returned to Nigeria.
Then, earlier this month, police tracked down the woman's estranged husband, Sam Onojhighovie. The 37-year-old Nigerian man had appeared at the High Court in Dublin as part of an ongoing attempt to extradite him to Germany, where he had been convicted in his absence and sentenced to seven years for offences linked to human trafficking. Scotland Yard officers visited him for questioning.
Of the 21 people arrested in the dawn raids last week 10 were illegal immigrants. None have been charged. Following the raids, Inspector O'Reilly said: "We are pretty confident we have a group of individuals who could have trafficked Adam into the country." Police are investigating a variety of offences, including benefit fraud, selling false passports and credit card and banking swindles. So far they are still some way off piecing together the exact fate of the boy they know as Adam.
"In West Africa there are several reasons for human sacrifices - for power, money, or to protect a criminal enterprise," said Inspector O'Reilly. "We believe the prime motive for the murder was to bring good fortune. We suspect Adam was killed to bring traffickers luck."
Police are waiting for the results of tests to compare the DNA of Sam Onojhighovie - and everyone arrested last week - with Adam's. If it shows that a terrible ritual murder was carried out to bring good fortune to an iniquitous scheme to traffic in human beings, there could be a grim final irony. The muti killing that was supposed to ensure the success of a criminal enterprise may actually have ensured its failure.