The practice has brought terror to parts of South Africa, where it is estimated that at least 300 people are killed each year for the medicine, known as muti.
One victim was Fortune Khumalo, a boy of nine, who was attacked as he relieved himself in bushes.
His attacker sliced off his penis and testicles to sell to a traditional healer in Johannesburg, where body parts can fetch £250 and a human head up to £500, according to the research for Channel 4’s Unreported World.
Fortune survived the attack but is in constant pain because his family cannot afford the reconstructive surgery he needs. His assailant was caught with the boy’s genitalia wrapped in a towel in his pocket.
Thomas Khumalo, Fortune’s father, said: “The killings are driven by greed. People believe using human body parts in medicine can make them rich.”
Special superintendent Gerard Labuschagne, an expert on ritual killings, said traditional healers are behind the killings, prescribing body parts to patients and hiring men to go out and find them.
Human genitals are the most prized parts and can be used to attract wealth and increase fertility. They are cooked and ground down for use with herbs and other ingredients.
Children’s body parts are thought to be the most potent and victims are often tortured first as the pain is believed to add to the power.
In the town of Bizana in Eastern Cape 18 people were murdered by a muti gang in nine months.
Vigilante gangs now patrol the area at night because they are concerned the police are not catching the culprits.
Bongani Danga, who leads the vigilantes, said: “People are really scared. Even with a police presence here, the killings continued so we decided we had to act to protect ourselves.”
Many muti murders go unreported but Supt Labuschagne admitted that even those which are reported may not be fully investigated.
“An investigative officer tasked to deal with this might be a bit hesitant because of his own traditional beliefs,” he said.