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 said 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.
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Italian news agency Ansa said Mr Medhanie was accused of being “the leader and organiser of one of the largest criminal groups operating between central Africa and Libya”.
The investigation is being led by investigators in Palermo, Sicily. Mr Medhanie is expected to appear in court on Wednesday.
The National Crime Agency said they tracked him down to an address in Khartoum, where he was then arrested.
British investigators had been supporting Italian officials looking into the Lampedusa tragedy.
The NCA said Mr Medhanie, 35, was known as The General, as he styled himself on the late Libyan leader Col Muammar Gaddafi.
The organisation said telephone intercepts acquired by Italian investigators showed Mr Medhanie co-ordinated journeys across the Mediterranean and across Africa to Libya.
In one recording, he is reportedly heard laughing at the deadly overloading of migrant boats.
“Medhanie is a prolific people-smuggler and has absolute disregard for human life,” said Tom Dowdall, the 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 Medhanie 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).
Up to 500 people were on the boat when it broke down 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.