Italian prosecutors are investigating whether the wrong man was extradited to Italy this week in a high-profile operation against people-smuggling.
A man thought to be suspected Eritrean people smuggler Mered Medhanie, 35, was seized in Sudan last month.
Two women said to be sisters of another Eritrean man, Medhanie Tesfarmariam Berhe, 27, say he was arrested instead.
One of them told the BBC of her shock at suddenly seeing photos of her missing brother in custody in Italy.
Italy announced the extradition on Wednesday, releasing video of a man in handcuffs being escorted off a plane.The country is currently at the forefront of the battle to stop smugglers sending tens of thousands of undocumented migrants on perilous journeys by boat to Europe.
Who was meant to be extradited?
Investigators say Mered Medhanie, dubbed The General, is responsible for the death of 359 migrants in October 2013.
They drowned when their boat sank off the Italian coast in October 2013.
He is alleged to have led a multi-billion dollar empire which specialised in smuggling migrants from Africa to Europe.
Mered Medhanie allegedly charged migrants up to €5,000 (£3,900; $5,680) for the trip.
What do the authorities say?
The UK’s National Crime Agency (NCA) said the man extradited had been arrested by Sudanese police with the help of the British and Italian authorities.
But after doubts were raised in the media about the suspect’s identity, Italian prosecutor Francesco Lo Voi announced that “checks” were being carried out.
“The identification of the suspect, his arrest, his handing over and his extradition to Italy were communicated to us in an official manner by the NCA and the Sudanese authorities through Interpol,” the Palermo prosecutor told Italy’s Ansa news agency.
The NCA said it was “too soon to speculate” about the identity claims but stressed it was “confident in its intelligence-gathering process”.
Who is Medhanie Tesfarmariam Berhe?
Medhanie Tesfarmariam Berhe is said to be an Eritrean asylum seeker who arrived in Sudan last year.