They first hit 10-year-old Sello Chokoe with a blunt instrument, causing a gash on his head. They then chopped off his penis, his hand and his ear. They were harvesting his body parts for "muti", the murderous practice of traditional African medicine.

Yet it is far from a normal part of such medicine. "In my many years of service in the South African police I have not encountered this sadistic taking of a young innocent life," said police inspector Mohlahla Moshane as he led us to the spot.

The murder site is a few kilometres from Sello's village of Moletjie in northern Limpopo.

Sello was lured to a lonely hill on the veld on the pretence of looking for a neighbour's donkeys.

After a carefully planned ambush, the killers wedged the boy between two large rocks to perform their macabre ceremony.

Sello dragged himself from the rocks where he had been abandoned and was found by a woman collecting firewood. He died a few days later in hospital.

The practice of muti provides a disconcerting counterpoint to the contemporary image of the new South Africa.

Dr Gerard Lubschagne, who heads the police investigative psychology unit, estimates lives lost to ritual murders at between 50 to 300 every year.

"We don't have accurate figures because most murders here are in our records as murders irrespective of motive," he says. "Most people might also not regard a murder as a muti matter but just dismiss it as the work of crazy killers."

Dr Lubschagne admits the rate of murders signals a worrying trend in South Africa. Despite South Africa being the most developed African economy, a huge chunk of its population still believes that power and wealth are better stoked by witchdoctors than stockbrokers.

"People who want to do better, people who want to be promoted at work, gamblers and politicians who want to win, even bank robbers who seek to get away with their criminal acts, turn to muti," Dr Lubschagne says.

Body parts are eaten, drunk or smeared over the ambitious person.

Various parts are used for different purposes. A man who had difficulty producing children killed a father of several children and used his victim's genitals for muti.

In another case, a butcher used a severed hand to slap each of his products every morning before opening as a way of invoking the spirits to beckon customers.

Mathews Mojela, the head teacher at Sello's school, has worked in rural areas for nearly a quarter of a century. He says muti is founded in the archaic belief that there is only a limited amount of good luck around - if you want to increase your wealth or luck then it should come at another's expense.

And the screaming of a child while his body parts are being chopped off is regarded as a sign calling customers to the perpetrator's business. It is also believed that magical powers are awakened by the screams. Eating or burying the body parts "captures" the desired results.

Robert Thornton, an anthropology professor at the University of Witswatersrand in Johannesburg, says children such as Sello are targeted because it is believed the power of the virgin is greater than that of a sexually active adult.

The main motivating idea is what Thornton describes as "symbolic logic" - the idea that another person's penis will strengthen that of the perpetrator, or that the perpetrator's farsightedness will be improved by devouring the victim's eyes. Blood is thought to increase vitality.

Professor Issack Niehaus of the University of Pretoria fears that muti killings will increase as the inequalities of wealth become more entrenched. "I would expect the occult economy - that is the belief in using magical means to gain prosperity - to increase as poverty worsens," Niehaus says.

One of the few victims who lived to tell his story is Jeffery Mkhonto. Six years ago, he was mutilated by an organised gang out to harvest body parts.

He had been lured to the house of a neighbour with an offer of food. Then he was castrated.

Lubschagne says muti killings are difficult to investigate because there is no clear relationship between perpetrator and victim.

Yet other reports suggest muti victims are often known to the perpetrators and therefore more easily lured - then mutilated and killed.

Neighbours are often too afraid to come forward with evidence because of fears of a magical retaliation.

At Sello's village, even the elders are too afraid to point the finger directly at one neighbour, traditional healer Peter Kagbi, although many villagers - in muffled tones - hint that he was implicated in Sello's murder.

Kagbi was thought to have sent Sello to fetch donkeys without Sello's mother's permission. Kagbi, who is in his late 60s, was questioned for four days by the police before being released pending further investigations.

Kagbi confirmed he had sent Sello to fetch the donkeys but denied taking part in the murder. He said he saw nothing wrong in sending Sello without permission as he had sent the boy on errands before - a point hotly disputed by the boy's family.

Kagbi said he had been threatened by neighbours and told they planned to burn him alive because he was a wizard.

"Some are accusing me of killing Sello but I did not," Kagbi said. "I have not fled my home despite the threats. If I do, the community will regard that as an admission of guilt."

Even the eventual capture and conviction of Sello's killers would do little for his brokenhearted single mother, Salome, 39, who lives with her two remaining children on the equivalent of $41 a month social welfare grant.

"Anything that does not bring back my son is hardly of any importance to me now," Salome says. "No mother wants to lose a child this way."

Her emotional state will not be helped when she learns that Sello's body parts were probably sold for no more than $550 each, the price usually charged for a child's body parts in the muti industry.