Italian authorities are leading the investigation into the sinking of the Bayesian superyacht – owned by British tech tycoon Mike Lynch – which has so far seen six people confirmed dead.
Mr Lynch’s body was among those recovered from the shipwreck, off the coast of Sicily, this week. His 18-year-old daughter, Hannah, is still missing.
Of the 22 people on board the Bayesian, 15 survived.
Here we look at how the superyacht’s capsizing, which happened in the early hours of Monday while anchored near Porticello, is being investigated.
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Who is investigating the sinking?
A criminal investigation was opened immediately after the tragedy, despite the fact no suspects have been identified publicly.
Investigators from the public prosecutor’s office in the Sicilian town of Termini Imerese are collecting evidence for that investigation.
The UK’s Marine Accident Investigation Branch (MAIB) has deployed a team of four inspectors to Italy to conduct a preliminary assessment.
It is understood they will look at all relevant aspects of the sinking, including the design, stability, and operation of the vessel. They will also examine the effects of the weather conditions experienced.
The MAIB does not look to establish blame or liability but seeks to discover the causes of accidents at sea and prevent similar incidents in future.
Witnesses to face ‘methodical’ questioning
The case is likely to carry on for months.
Investigators will take their time, speaking to survivors and eyewitnesses, as well as examining physical evidence.
They have already started to question witnesses, including the vessel’s captain James Cutfield.
Obtaining witness testimony as soon as possible will be key for the authorities investigating the disaster, according to experts.
James Wilkes, a marine investigator, told Sky News those examining the sinking will want to speak to those who survived or saw what happened “while the memories are fresh in their mind”.
“Fortunately, 15 people survived,” he said.
“I’d like to explore the circumstances in which they were able to survive the storm and the sinking, to look at the anomalies and work out the difference between those and the people that sadly didn’t survive, and combine it all with technical data and simulation.”
Mr Wilkes added investigators must work through evidence “methodically and meticulously”.
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Will the shipwreck form part of the investigation?
Questions have been raised about whether the sunken yacht will be salvaged during the investigation.
The Italian coastguard has said a decision on whether to raise the vessel from the seabed was “not a topic on the agenda” at the moment – but “will be” in the future.
Nick Barke, head of salvage operations at Boats.co.uk, a boat sales and services company, said the “only real way of knowing” why the yacht sank would be to lift it to the surface.
The Bayesian had an extractable keel (an underwater fin) that was almost 10 metres in length when extended and acted as a counterbalance for the vessel.
Its final position will be crucial for investigators to discover.
If it was stowed when the storm hit, it would have made the yacht much less stable.
“That is a key fact that needs to be established,” Matthew Schnack, chairman of the Maritime Search and Rescue Council, told Sky News.
“That keel in effect will lower the centre of gravity of the vessel and make it more stable.
“And if that keel was lifted up, it could have had significant impact on the vessel’s ability to stay upright when the storm hit.”
Investigators are also likely to look at whether any openings – such as windows and doors – were open on the vessel, which could have allowed it to fill with water more quickly.
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Questions raised about human error
The chief executive of a firm which makes and sells yachts like the Bayesian believes the sinking may have been due to a series of human mistakes.
Giovanni Constantino, CEO of the Italian Sea Group, told Sky News the storm on Monday had been expected.
Mr Costantino asked: “Why was the ship in that situation? The storm was readable… We must ask ourselves why none of the fishermen in the port of Porticello went out at sea that night? Why did no one go out to sea?
“Everyone knew about the storm. And then, if a fisherman knew, why the commander of a ship of such importance, with guests of such level and importance, with 12 guests on board… Why wasn’t he in an alert situation?”
Mr Constantino had earlier told Sky News there were no flaws with the design and construction of the Bayesian and vessels like the stricken superyacht were “unsinkable”.
The chief executive has also been pushing the same message to Italian media outlets.
“A Perini boat survived the Category 5 Katrina hurricane. Do you think one couldn’t survive a waterspout here?” he told the Corriere della Sera newspaper, referring to a type of tornado which is believed to have hit the Bayesian.
But as well as the possibility of human mistakes, investigators will also look at whether the yacht was technically sound, and how rare the tornado weather event was which led to the sinking.
