Hunting down those who kill people to sell their body parts for 'magic charms'

One member of our team went undercover, using the name Osman, to pose as a politician who wanted to achieve power through human sacrifice.

We first travelled to a remote area of Kambia district, in the north of the country near the Guinean border, to meet the juju man in his secret shrine - an area in dense bush where he consulted with his clients.

Calling himself Kanu, he wore a ceremonial red mask covering his whole face to conceal his identity and boasted of his political connections.

"I was working with some big, big politicians in Guinea, Senegal and Nigeria. We have our team. Sometimes during election time, at night, this place is full of people," he claimed.

Election season is regarded by some as a particularly dangerous time when parents have been warned to take special care of their children because of the heightened risk of abductions.

On a second visit, Kanu became more confident and showed Osman what he said was evidence of his trade - a human skull.

"You see this? This belongs to someone. I dried it for them. It is a woman's skull. I am expecting the person to pick this up today or tomorrow."

He also pointed to a pit behind his shrine: "This is where we hang human parts. We slaughter here, and the blood goes down there… Even big chiefs, when they want power, come here. I give them what they want."

When Osman specified that he wanted limbs from a woman to be used in a ritual, Kanu got down to business: "The price of a woman is 70m leones [£2,500; $3,000]."

Osman told him not to proceed yet but when he later received a call from Idara claiming his team had identified a victim, we contacted Police Commissioner Ibrahim Sama.

He decided to organise a raid - but said his officers would not do so without the involvement of Mr Tarawallie, who often assists the police on such operations.

"When we got intelligence that there is a particular dangerous witchdoctor operating a shrine, we will work with the traditional healers," said an officer on the raid, Assistant Superintendent Aliu Jallo.

He went on to express the superstitions some officers have about tackling rogue herbalists: "I will not go and provoke situations. I know that they have their own powers that are beyond my knowledge."

After Idara was captured - discovered hiding in the roof clutching a knife - Mr Tarawallie began searching the property for evidence, saying there were human bones, human hair and piles of what looked like dirt from cemeteries.

This was enough for the police to arrest Idara and two other men, who were charged in June with practising sorcery as well as being in possession of traditional weapons used in ritual killings. They pleaded not guilty to the charges and have since been granted bail, pending further investigations.