Groundbreaking forensic work has revealed that the boy, who has been named Adam by officers, came from a particular part of south-west Nigeria.

Detectives will travel within the next few weeks to the rural area between Benin City and Ibadan, which is a 100 mile by 50 mile corridor.

The boy, who was between four and seven years old, was discovered in the river near Tower Bridge in September 2001.

A few months ago we were working on Adam being from somewhere in five countries in West Africa and to narrow it down to such a smaller area is remarkable Detective Inspector Will O'Reilly

When his body was found, it prompted a major police inquiry reaching as far as South Africa.

Police believed the boy may have been subject to a West African-style "muti" ritual killing, commonly associated with South Africa.

After samples taken from Adam's bones showed traces of a particular type of pre-Cambrian rock from West Africa a team from Scotland Yard travelled to Nigeria and took 100 samples from a 10,000 square kilometre area.

They were taken from sources such as soil, rocks, elephants, bush meat, wild game and human post-mortem examinations.

Further tests

By looking for the pre-Cambrian rock similar to those found in Adam, Professor Ken Pye, a forensic geologist, was able to discount 95% of Nigeria and establish where the boy came from.

Detective Inspector Will O'Reilly, who travelled to Nigeria to collect samples, said: "A few months ago we were working on Adam being from somewhere in five countries in West Africa and to narrow it down to such a smaller area is remarkable."

The area could be further narrowed when tests are carried out on the lead levels in Adam's torso which will establish whether or not he lived in a polluted urban area.

Former South African president Nelson Mandela made an appeal for information which will be translated into Woruban, the local language, and posters will go up in the area.

DNA test

A �50,000 reward is already on offer for information leading to the conviction of Adam's killers and a second reward of �2,500, in local currency, is being offered for information leading to his identification.

Police are concerned that the huge amount by local standards may attract fraudsters claiming to be Adam's parents.

Anyone who comes forward will be DNA tested against samples taken from the boy.

Further forensic work is also being carried out on a concoction found in Adam's lower gut which he is thought to have swallowed before he was sacrificed.

It is thought to contain quartz, bone, clay pellets and very small samples of rough gold.

Scientists believe they may be able to source where the gold came from and are also trying to identify what species the bones were from.

They already know from pollen samples found in Adam's stomach that he was alive when he got to London.