ROME (Reuters) -Seven people are believed to have died, including British tech tycoon Mike Lynch and Morgan Stanley's Jonathan Bloomer, after a luxury yacht belonging to Lynch's family sank off the northern coast of Sicily on Monday.
Here is what we know about the Aug. 19 accident.
VIOLENT STORM
The Bayesian, a British flagged 56-metre (184-feet) superyacht, sank in the dark shortly before 5 am (0300 GMT) off the port of Porticello, near Palermo, after being hit by a "violent storm," the Italian coast guard said.
The coast guard said bad weather had been forecast, but added that it was more virulent than expected.
Some locals spoke of a waterspout, or sea whirlwind, of exceptional force.
THE OTHER BOAT
The nearby yacht, the 42-metre Sir Robert Baden Powell, remained anchored and weathered the storm after its captain turned on the engine to keep control and avoid a collision with the Bayesian.
The captain, Karsten Borner, said he did not know if the crew of the Bayesian had managed to switch on its engines.
"I only know that they went flat with the mast on the water and that they sank in two minutes," he said.
'INCOMPREHENSIBLE'
Andrea Ratti, a nautical design professor at Milan Polytechnic university, said a boat the size of the Bayesian could only sink so rapidly by taking in a huge amount of water.
He suggested that one or more portholes, windows or other openings may have been left open, broken or smashed by the waterspout, letting in water.
However, an industry expert in Britain said it should have taken hours for the Bayesian to fill up with enough water to sink it, making its swift demise incomprehensible.
Matthew Schanck, chair of Britain's Maritime Search and Rescue Council, said the Bayesian was the victim of a so-called black swan, a rare event with a high impact.
RECORD MAST
The Bayesian featured the world's tallest aluminium mast, measuring 72 metres.
A tall mast has a lot of surface area exposed to the wind, but Ratti and structural engineer Filippo Mattioni said it is not by itself an element of vulnerability in a storm.
Fire department diver Marco Tilotta said the wreck was intact and the mast was still attached. He added, that divers had not been able to inspect the full length of the mast but the section they had seen was undamaged.
RETRACTABLE KEEL
The Bayesian had a retractable keel - a stabilising structure under the hull which can be partially lifted to reduce the depth of the ship when entering shallow waters or harbours.
Both Ratti and Mattioni wondered if the yacht had been anchored with the keel up, compromising its stability in a violent storm.
UNSINKABLE
The Bayesian was built in 2008 by Perini Navi, an Italian luxury yacht maker. It was refitted twice but not by Perini, a source with knowledge of the matter told Reuters.
Giovanni Costantino, CEO of the Italian Sea Group, which owns Perini, said the yacht was "one of the safest boats in the world" and basically unsinkable.
He added that its sinking was due to a chain of human errors given that the storm was expected, speaking in interviews to Italian media.
Had the crew shut all doors and hatches, turned on the engine, lifted the anchor, lowered the keel and turned the yacht to face the wind, they would have suffered "zero damage", the CEO said.
He added that data showed it took 16 minutes from when the wind began buffeting the yacht, and it began taking on water, for it to sink.