Officers believe the boy, who they have named Adam, may have come from West Africa.

They fear the unidentified child, aged between four and six, was the victim of a sacrificial killing.

His torso was discovered near Tower Bridge in September 2001.

Police want to find Adam's real identity and hope to trace his parents.

Four Scotland Yard detectives will spend the next month on house-to-house inquiries in 1,000 Nigerian villages.

Clues

They have already been told about one child who went missing from a village in Oyo state at the relevant time.

Anyone claiming to be Adam's parents will be DNA tested.

The body was found without head or limbs

Nigerian police have begun to compile a dossier on ritual killings so that can investigate them more thoroughly.

Forensic evidence has already suggested the boy had strong links with a rural area in south-western Nigeria between Benin City and Ibadan, which is a 100 mile by 50 mile corridor.

Local mineral samples taken last year by scientists are said to match those found in Adam's body.

A �50,000 reward is already on offer for information leading to the conviction of his killers.

A second reward of �2,500, in local currency, is being offered for information leading to the boy's identification.

Last year former South African president Nelson Mandela made an appeal for information.