The Italian coast guard said on Thursday the body of British tech magnate Mike Lynch is among those recovered off the coast of Sicily from the wreckage of a superyacht whose builders had called unsinkable.

One woman remains missing. She has not been identified, but Hannah Lynch, Lynch's 18-year-old daughter, is reportedly unaccounted for. The family had been celebrating his recent acquittal on fraud charges with the people who defended him at trial in the United States.

Five others were recovered by rescue crews following on Monday's tragedy.

The Bayesian, a 56-meter (184-foot) British-flagged yacht, went down in a storm early on Monday as it was moored about a kilometer (half a mile) offshore. Civil protection officials said they believe the ship was struck by a tornado over the water, known as a waterspout, and sank quickly.

Termini Imerese Public Prosecutor’s Office investigators were collecting evidence for a criminal investigation, which they opened immediately after the tragedy despite no formal suspects having been publicly identified.

The chief executive of The Italian Sea Group, which owns the Bayesian's manufacturer, told AP in an interview on Thursday that superyachts like these are “designed to be unsinkable."

“And it is unsinkable not only because it is designed in this way, but also because it is a sailing ship and sailing ships are the safest ever,” CEO Giovanni Costantino said.

Costantino added that “obviously they must not hit the rocks violently, discarding the hull, and they must not take in water,” suggesting the second possibility was the most likely in this case.

Costantino also noted that sailing ships require “a greater competence” to be guided compared with motor boats.

Investigators are now looking at why the Bayesian, built in 2008 by Italian shipyard Perini Navi, sank while a nearby sailboat remained largely unscathed. Fifteen of the 22 people aboard survived by escaping in a lifeboat, including a mother who reported holding her 1-year-old baby over the waves to save her. They were rescued by the sailboat Sir Robert Baden Powell.

The sailboat's captain, Karsten Borner, said his craft sustained minimal damage — the frame of a sun awning broke — even with winds that he estimated had reached 12 on the Beaufort wind scale, the highest hurricane-strength force on the scale.

He said he had remained anchored with his engines running to try to maintain the ship’s position as the forecast storm rolled in.

“Another possibility is to heave anchor before the storm and to run downwind at open sea,” Borner said in a text message. But he said that might not have been possible for the Bayesian, given its 75-meter (246-foot) tall mast.

“If there was a stability problem, caused by the extremely tall mast, it would not have been better at open sea,” he said.

Yachts like the Bayesian are required to have watertight compartments that are specifically designed to prevent a rapid, catastrophic sinking even when some parts fill with water.

Lynch is the only person confirmed dead; the other bodies have not been formally identified by the Italian coast guard.

Besides Hannah Lynch, those missing are Christopher Morvillo, one of Lynch’s U.S. lawyers, and his wife, Neda; Jonathan Bloomer, chairman of Morgan Stanley’s London-based investment banking subsidiary, and his wife, Judy.

The body of chef Recaldo Thomas was the first to be recovered, on Monday. His death was confirmed by his family.

Divers have struggled to find the bodies in the yacht’s hull on the seabed 50 meters (164 feet) underwater.

“We would need a crystal ball to know when we'll be able to find the next body," said Luca Cari, spokesperson for the fire rescue service.

“It's very difficult to move inside the wreckage. Moving just one meter can take up to 24 hours,” Cari said.