The body of British tech magnate Mike Lynch was recovered on Thursday from the wreckage of his family yacht that sank this week off the coast of Sicily during a violent storm, a senior Italian official said.

Lynch's 18-year-old daughter Hannah is still unaccounted for, Interior Ministry official Massimo Mariani told Reuters after being briefed by the emergency services.

The British-flagged Bayesian, a 56-metre-long (184-foot) superyacht carrying 22 passengers and crew, was anchored off the port of Porticello, near Palermo, when it disappeared beneath the waves in minutes after bad weather struck early Monday.

Lynch, 59, was one of the U.K.'s best-known tech entrepreneurs sometimes referred to as the country's answer to Bill Gates.

He had invited friends to join him on the yacht to celebrate his acquittal in June in a U.S. fraud trial.

Seven people are believed to have died in the disaster while 15 survived, including Lynch's wife, Angela Bacares, who is the owner of the Bayesian.

They survived by escaping in a lifeboat, with Bacares reportedly holding her 1-year-old baby over the waves to save her. They were rescued by the sailboat Sir Robert Baden Powell.

Civil protection officials said they believe the ship was struck by a tornado over the water, known as a waterspout, and sank quickly.

Recovering last body could take time

Italian officials confirmed on Wednesday they had retrieved the bodies of Jonathan Bloomer, a non-executive chair of Morgan Stanley International, and Christopher Morvillo of the law firm Clifford Chance, alongside their wives, Judy Bloomer and Neda Morvillo.

"This is an unimaginable grief to shoulder," the Bloomer family said in a statement Thursday.

Jonathan and Judy "were incredible people and an inspiration to many, but first and foremost, they were focused on and loved their family and spending time with their new grandchildren," it said.

"Together for five decades, our only comfort is that they are still together now."

The body of the onboard chef, Canadian-Antiguan national Recaldo Thomas, was recovered near the wreck on Monday.

Mariani said it was possible that Hannah Lynch's body was not in the boat, but might have been swept out to sea.

Fire brigade spokesperson Luca Cari said if her body was still in the yacht it could take time to find, given the difficulty divers were having in accessing all areas of the boat, which is lying on its side at a depth of 50 metres (165 feet).

Sinking blamed on crew errors

A judicial investigation has been opened into the disaster, which has baffled naval marine experts, who say a boat like the Bayesian, built by Italian high-end yacht manufacturer Perini, should have withstood the storm.

Investigators are now looking at why the Bayesian, built in 2008, sank while a nearby sailboat remained largely unscathed.

Giovanni Costantino, CEO of the Italian Sea Group, which owns Perini, told Italian media the Bayesian was "one of the safest boats in the world" and blamed the crew for failing to follow correct safety procedures.

Costantino claimed 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," he separately told The Associated Press (AP) on Thursday.

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.

The captain, James Cutfield, and his eight surviving crew members, have made no public comment on the disaster.

The prosecutor leading the investigation, Ambrogio Cartosio, has scheduled a press conference for Saturday.

Sailboat Sir Robert Baden Powell'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 told AP 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.

Challenging conditions

Specialist rescuers have been searching inside the hull of the sunken yacht for the past three days. They said the conditions were extremely challenging due to the depth and the narrowness of the places that the divers are scouring.

The fire brigade compared the efforts to those that were carried out, on a larger scale, for the Costa Concordia, a luxury cruise liner that capsized off the Italian island of Giglio in January 2012, killing 32 people.

Once the final body is recovered, experts will have to decide whether, or how, to salvage the vessel.

The CEO of Italian Sea Group said the yacht's automatic tracking system suggested that it took 16 minutes from the moment the storm first hit to the sinking.

He said it was clear the ship took in large amounts of water, adding that investigators would need to see what doorways or hatches might have been left open, focusing notably on a main door located on the left side of the yacht.

"A Perini boat survived the Category 5 Katrina hurricane. Do you think one couldn't survive a waterspout here," he told Corriere della Sera newspaper, referring to a type of tornado that is believed to have hit the Bayesian.

Under maritime law, a captain has full responsibility for the ship and the crew, as well as the safety of all those aboard.

The captain of the Costa Concordia, Francesco Schettino, is serving a 16-year prison term for his role in the 2012 disaster after he admitted to sailing too close to underwater rocks.