An Italian prosecutor has opened a manslaughter investigation into the deaths of British technology magnate Mike Lynch and six other people who died when a luxury yacht sank off Sicily this week.

The Termini Imerese Public Prosecutor’s Office, led by Ambrogio Cartosio, announced the investigation but stated that the investigation was not directed against any single person.

Lynch’s 18-year-old daughter Hannah was among those killed when the family’s 185-foot (56-meter) boat, the Bayesian, capsized off Porticello, near Palermo, during a violent storm before dawn on Monday.

Fifteen people survived, including Lynch’s wife, whose company owned the Bayesian, and the yacht’s captain.

Captain James Cutfield and the other survivors were interviewed by the Coast Guard on behalf of the prosecution. None of them have publicly explained how the ship sank.

Hannah Lynch’s body was discovered on Friday by divers who had been searching the sunken ship for the past five days. The five other dead passengers were recovered on Wednesday and Thursday, while the body of the only deceased crew member, ship’s cook Recaldo Thomas, was found on Monday.

The sinking has puzzled marine experts, who believe that a boat like the Bayesian, built by Italian luxury yacht builder Perini, should have withstood the storm and should not have sunk as quickly as it did.