British police believe they may have smashed a gang of child traffickers after a series of dawn raids triggered by the inquiry into the murder of a child whose torso was found floating in the River Thames.
An animal skull with a nail driven through it was allegedly found at one of the London addresses raided, as well as samples of clay and soil which may be evidence of the practice of traditional west African rituals.
Police believe the boy found in the Thames was brought to London by traffickers with the intention of being sacrificed in an occult ritual.
A potion containing bone fragments, clay pellets, quartz and small amounts of rough gold was found in his stomach after his body was discovered near Tower Bridge two years ago.
The arrests of 21 people in London Tuesday follow the arrest of a woman a year ago in Glasgow in connection with the murder and with the recent detention of a convicted human trafficker in Dublin.
Detective Inspector Will O'Reilly, heading the murder inquiry, said: "We believe these may be people who made considerable amounts of money from trafficking into the UK. These people are potentially linked to the arrests in Scotland and in Ireland."
Police said the group was being investigated for trafficking offences rather than murder. But it is suspected that one of those arrested may have brought the boy, to whom police have given the name Adam, to Britain.
"If we find out that these people have trafficked Adam, we can do some further inquiries on that," O'Reilly said.
The raids involved more than 200 officers who targeted nine addresses in east and south-east London during the early hours of the morning.
Most of those detained are believed to be in their 20s and 30s and are Nigerian nationals. They were arrested on suspicion of immigration, people trafficking, and passport offences. Police do not know how many children have been involved with the trafficking ring.
One of the women arrested was nursing a baby, which is now being cared for.
Detectives said there was evidence indicating children had been present at some of the addresses, although these were addresses through which a number of people had passed.
Commander Andy Baker, who is overseeing the Adam inquiry, said children brought into Britain on false documents were often used to carry out benefit fraud, or forced to work as "slave" labor or in the sex industry.
Many arrive at British airports travelling alone and escape the attention of the authorities because they are travelling on British passports which are either stolen or forgeries.
Detectives believe the children are given false identities and are passed around adults claiming to be their parents, who make bogus child benefit claims.
The group arrested yesterday will be DNA tested to see if there is any family link with Adam. Detectives have established Adam was from a region of south-west Nigeria between Benin City and Ibadan. Most of those arrested yesterday are believed to be from the Benin City area.