ROME — Prosecutors in Italy said Saturday they have opened an investigation into shipwreck and manslaughter after a superyacht capsized during a storm off the coast of Sicily, killing seven people onboard.

Termini Imerese prosecutor Ambrogio Cartosio confirmed the investigation but said no suspect is currently identified.

“We are only in the initial phase of the investigation. We can’t exclude any sort of development at present,” he told reporters at a news conference.

The main question investigators are focusing on is how a sailing vessel deemed “unsinkable” by its manufacturer, Italian shipyard Perini Navi, sank while a nearby sailboat remained largely unscathed.

Rescuers on Friday brought ashore the last of seven bodies from the sinking of The Bayesian, a 56-meter (184-foot) British-flagged luxury yacht that went down in a storm near the Mediterranean island in southern Italy early Monday. The sailboat was carrying a crew of 10 people and 12 passengers.

The body was believed to be that of Hannah Lynch, 18, the daughter of British tech magnate Mike Lynch. His body was recovered Thursday. He had been celebrating his recent acquittal on fraud charges with his family and the people who had defended him at trial in the United States. His wife, Angela Bacares, was among the 15 survivors.

Civil protection officials said they believe the yacht, which featured a distinctive 75-meter (246-feet) aluminum mast, was struck by a tornado over the water, known as a waterspout, and sank quickly.

Rescuers struggled for four days to find all the bodies, making only slow headway through the interior of the wreck lying on the seabed 50 meters (164 feet) below the surface.

“The Lynch family is devastated, in shock and is being comforted and supported by family and friends. Their thoughts are with everyone affected by the tragedy,” a spokesperson for the family said in a statement issued Friday.

The other five victims 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; and Recaldo Thomas, the yacht’s chef.