Italian rescue divers have found the body of the last person missing after British technology magnate Mike Lynch’s family yacht sank off Sicily. It is believed to be his daughter Hannah, a source familiar with the matter told Reuters on Friday.

The British-flagged Bayesian, a 56-metre luxury sailing boat carrying 22 passengers and crew, was anchored off the harbour of Porticello near Palermo when it capsized and sank rapidly in a pre-dawn storm on Monday.

While the source did not identify the body as that of 18-year-old Hannah Lynch, she was the only person whose whereabouts were still unknown. Italian news agency Adnkronos reported that she was found inside the yacht.

The wreck lies at a depth of 50 metres and the passageways are narrow. The fire service described the rescue work on Friday as “lengthy and delicate” and said that more than 400 people, including 28 specialist divers, were involved.

The bodies of the other five dead passengers, including Lynch, were recovered from inside the yacht on Wednesday and Thursday. The body of the only deceased crew member, ship’s cook Recaldo Thomas, was found near the wreck on Monday.

Official identification of the bodies and autopsies are expected to begin after the last recovered body is transferred to the morgue of a hospital in Palermo.

A judicial investigation has been launched into the sinking of the ship, which has baffled marine experts who believe that a boat such as the Bayesian, built by Italian luxury yacht builder Perini, should have withstood the storm.

The yacht’s captain, James Cutfield, his eight surviving crew members and passengers have been questioned by police but have not made any public statements. Investigating prosecutors will hold a press conference on Saturday.

Giovanni Costantino, CEO of Italian Sea Group, which owns Perini, told Reuters the shipwreck was the result of a series of “indescribable, unreasonable errors” by the crew and ruled out design flaws.

Pulling the wreckage out of the sea, where it now appears to be lying intact on its right side, could help investigators figure out what happened, but the operation is likely to be complex and expensive.

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

He told the daily newspaper “La Repubblica” that the salvage of the yacht, including the preparatory work, would take six to eight weeks and would have to be completed by mid-October. However, he did not give any reasons for this timing.

Raising the yacht to the surface would have to be done “very, very slowly” and could take several days, he said.