Detectives investigating the murder of a boy whose torso was found in the Thames have arrested a gang suspected of bringing children into the UK illegally.
More than 200 officers raided nine addresses in east and south-east London.
Thirteen people have been arrested on suspicion of immigration and people trafficking offences.
Police believe the 13, all Nigerian nationals, are involved in bringing children and adults from west Africa to the UK via Europe.
It is the route they suspect was followed by the boy found at Tower Bridge in September 2001.
He was named Adam by detectives and was between four and seven-years-old. He had been mutilated in what police believe was a ritualistic sacrifice, possibly by the African black magic "muti" cult.
Commander Andy Baker, of Scotland Yard, said everyone arrested in the operation would be DNA tested to see if there was any family link with Adam.
Mr Baker said children brought into the UK on false documents are often used to carry out an elaborate benefit fraud or even as "slave" labour.
A small number may end up in the sex industry, he added.
Detective Inspector Will O'Reilly, leading the Adam inquiry, said: "We have searched nine addresses across London looking for the organisers of this criminal gang.
"We don't know how many children are involved in this operation but it's certainly in the hundreds, if not the thousands, coming from mainland Africa into the UK."
Detectives used groundbreaking forensic techniques to establish that Adam was from a region of south west Nigeria between Benin City and Ibadan.
The majority of those arrested today were believed to be from the Benin City area of the country.
Earlier this month, a Nigerian man was interviewed by police in connection with Adam's death.
Sam Onojhighovie, 37, appeared at Dublin's High Court as part of a bid to extradite him to Germany, where he has already been convicted in his absence and sentenced to seven years for offences linked to human trafficking.
Detective Inspector O'Reilly has spoken to Onojhighovie and requested a DNA test, believing he could be the boy's natural father.
He is thought to be the estranged husband of Joyce Osagiede, who was arrested in connection with the murder a year ago in Glasgow.
She was not charged and was later returned to Nigeria.