Police raided nine homes across London

The 10 men and 11 women were arrested on Tuesday in raids at nine addresses in east and south-east London.

Most of those arrested were Nigerian and were held for immigration offences and suspected identity fraud and passport forgery.

The police were acting on information from detectives who have been investigating how the limbless and headless body of a boy ended up in the Thames in London.

The victim, called Adam by officers, was found in the river near Tower Bridge in September 2001.

Police suspect he was a victim of ritual killing after being brought over from Nigeria.

Detective Inspector Will O'Reilly, leading the Adam inquiry, said: "We've uncovered what we believe is a criminal network concentrating on people trafficking.

'Trafficking ring'

"We are convinced that we are on to a group, or individuals, that were involved in trafficking Adam into the country."

Officers travelled to the African country after forensic tests showed Adam was from the area around Benin City.

All of the people arrested on Tuesday are believed to be from the same part of Nigeria, and police want to compare their DNA with Adam's to see if any are related to him.

CRIMINAL NETWORK We are convinced that we are onto a group or individuals that were involved in trafficking Adam into the country Detective Inspector Will O'Reilly Watch the police news conference

Police also said there was evidence of children having been at the raided addresses.

A baby belonging to one of the women was also taken into care while the woman was being questioned.

Police said they found several "interesting" items in the raids, including what appeared to be the skull of an animal which had a nail driven through it.

Commander Andy Baker, from the Metropolitan Police, said: "Some of the items would raise a few eyebrows - they look like some element of ritualism is involved."

Police are also looking at their connection with a Nigerian man arrested in Dublin earlier this month in connection with the investigation.

Sam Onogigovie, 37, was held under an extradition warrant issued by police in Germany, where he has been convicted of crimes linked to human trafficking.

Detectives from Scotland Yard also questioned him about the murder of Adam.

Tuesday's arrests were made by officers from Operation Maxim, the multi-agency unit tasked with targeting organised criminals who are in the UK illegally.

The body was found without a head

Detectives think Adam was aged between four and six, and was alive when he arrived in London.

They are also trying to trace the witch doctor who brewed a potion containing bone fragments which the boy swallowed before he died.

The fragments have been submitted to New York's medical examiner who will use techniques developed to identify September 11 victims.

Some substances found in the raids will be compared with the potion found in Adam's intestines.