Italian divers have retrieved the body of British tech magnate Mike Lynch’s 18-year-old daughter, Hannah, who was the last person still unaccounted for after the family’s luxury yacht sank this week off Sicily.

Seven people, including Lynch himself, died when the 56-metre-long (184-foot) sail boat, the Bayesian, capsized during a fierce, pre-dawn storm on Monday off Porticello, near Palermo. Fifteen people survived, including Lynch’s wife and the yacht’s captain.

Lynch’s family is devastated and in shock, a spokesperson for the family said on Friday, in their first public comments since the yacht sank.

“Their thoughts are with everyone affected by the tragedy. They would like to sincerely thank the Italian coastguard, emergency services and all those who helped in the rescue,” the statement said.

“Their one request now is that their privacy be respected at this time of unspeakable grief.”

Prosecutors in the nearby town of Termini Imerese are looking into possible human error that might have led to the disaster. As of yet, nobody has been placed under formal investigation and none of the survivors have commented publicly.

Hannah Lynch’s body was discovered on Friday by specialist divers who have been scouring the submerged vessel for the past five days, a senior official with knowledge of the rescue operation said, declining to be named.

The five other dead passengers were recovered on Wednesday and Thursday. The body of the only crew member who died, onboard chef Recaldo Thomas, was found near the wreck on Monday.

Official identification of the corpses and autopsies will take place in Palermo.

The sinking has puzzled naval marine experts who say a boat like the Bayesian, built by Italian high-end yacht manufacturer Perini, should have withstood the storm and should not, in any case, have sunk as quickly as it did.

The yacht’s captain James Cutfield, his eight surviving crew members and passengers have been questioned by the coast guard on behalf of prosecutors. Investigators are due to hold a news conference on Saturday.

Giovanni Costantino, CEO of The Italian Sea Group that owns Perini, told Reuters the shipwreck was the result of a string of “indescribable, unreasonable errors” made by the crew, and ruled out any design or construction failings.

The Bayesian is lying on its side, apparently intact at a depth of 50m (164 feet). Pulling it out of the sea may help investigators determine what happened, but the operation is likely to be complex and costly.

Nick Sloane, a South African engineer who led the operation to salvage the Costa Concordia cruise liner that sank in 2012, said in Italian media interviews on Friday that the operation would cost up to 15 million euros (US$16.7 million).

He told daily La Repubblica that salvaging the yacht would take six to eight weeks, including preparation work, and would have to be completed by mid-October, without specifying the reasons for the timing.

Bringing the yacht to the surface will have to be done “very, very slowly”, and might take a couple of days, he said.

Lynch, 59, was one of Britain’s best-known tech entrepreneurs and had invited friends to join him on the yacht to celebrate his acquittal in June in a US fraud trial.

Among those who died in the wreck were Lynch’s lawyer Chris Morvillo and Jonathan Bloomer, a Morgan Stanley banker who had appeared as a character witness in the case on his behalf.

Lynch’s wife Angela Bacares headed the company that owned the boat.