An Eritrean man believed to be at the heart of the operation to smuggle migrants from Africa to Europe has been extradited to Italy, prosecutors say.
Mered Medhanie, known as The General, was held in Sudan in May and was flown to Rome on Tuesday.
Britain's National Crime Agency says he is thought to have arranged the transit of a boat that sank near the Italian island of Lampedusa in October 2013.
At least 359 migrants died when the boat, travelling from Libya, capsized.
Most were from Eritrea and Somalia.
Italian news agency Ansa said Mr Mered was accused of being "the leader and organiser of one of the largest criminal groups operating between central Africa and Libya".
Prosecutors accuse Mr Mered of running the network alongside an Ethiopian accomplice, who is still at large.
The two men are accused of buying up kidnapped migrants from other gangs and sending those migrants on barely seaworthy ships across the Mediterranean towards Europe.
The investigation is being led by investigators in the Sicilian city of Palermo. Mr Mered is expected to appear in court on Wednesday.
The UK's National Crime Agency said it had tracked him down to an address in Khartoum, where he was then arrested. The rare extradition from Sudan to Italy was completed in record time, reported Italy's La Repubblica (in Italian).
Profile of people-smuggling 'kingpin':
- The 39-year-old Eritrean once lived in Italy, where he came under the radar of anti-mafia investigators after trying to open a bank account in Dubai
- Later moved to Libya, where most African migrants start the treacherous journey to Europe, and finally to Sudan, where he was arrested
- His wife and family live in Sweden
- Called "the General", as he styled himself on late Libyan leader Col Muammar Gaddafi
- Said to have driven around in a tank and boasted: "Nobody is stronger than me"
- Amount of money that went through him estimated in the billions
British investigators had been supporting the Italian inquiry into the Lampedusa tragedy.
La Repubblica says telephone intercepts acquired by Italian investigators depict a man who, while kind and considerate when dealing with matters relating to his wife and children in Sweden, was cynical and ruthless in his work.
'Disregard for life'
In the recordings, he estimates he has smuggled 7,000 or 8,000 people. In one, he is reportedly heard laughing at the overloading of migrant boats.
A key concern was where to hide his spoils. The best place would be America or Canada, he is quoted as saying: "there, they don't ask where you got it from."
"Medhanie is a prolific people-smuggler and has absolute disregard for human life," said Tom Dowdall, deputy director of the NCA.
"Although he was operating thousands of miles away, his criminal activity was impacting the UK. Medhanie no doubt thought he was beyond the reach of European justice but we were able to support the Italians by tracking him down to Sudan."
Italy's Corriere Della Serra newspaper reported that Mr Mered boasted of being in league with local officials in Tripoli, Libya, while also having a network of workers in Italy.
He charged migrants up to €5,000 (£3,900; $5,680) to travel from African countries to northern Europe, the newspaper said (in Italian).
Investigators are said to be hopeful that he will co-operate with the investigation, helping to identify other smugglers carrying people on the Libya-Italy route.
Up to 500 people were on the boat which broke down and then sank in early October 2013.
Those who survived said that some of those on board set fire to a piece of material to try to attract the attention of passing ships, only to have the fire spread to the rest of the boat.
In 2014, the year after the Lampedusa tragedy, the number of migrant arrivals to Italy jumped to 170,000, before dropping to 153,800 last year. Close to 40,000 people have arrived in Italy so far this year.