Sicilian prosecutors said Saturday they were investigating potential crimes of negligent shipwreck and manslaughter after a superyacht sank killing seven people, including UK tech tycoon Mike Lynch.
Prosecutors stressed the investigation was at an early stage following the sinking of the British-flagged "Bayesian" off the north of the Italian island in a storm on Monday.
"The Public Prosecutor's Office of Termini Imerese has registered a file with the state against unknown persons, hypothesising the crimes of negligent shipwreck and multiple negligent manslaughter," state prosecutor Ambrogio Cartosio told reporters.
But he cautioned that with last body -- Lynch's 18-year-old daughter Hannah -- having only been recovered on Friday, the probe was at an early stage.
He said he was only speaking publicly due to the huge international interest in the case.
"We are only in the initial phase of the investigations... At this stage, precisely because the investigation could develop in any way, we are absolutely not ruling anything out," he said.
Lynch, 59, had invited friends and family onto the boat to celebrate his recent acquittal in a massive US fraud case.
But the 56-metre (185-foot) yacht was struck by something akin to a mini-tornado before dawn on Monday as it was anchored off Porticello, near Palermo.
Fifteen people were rescued and the body of one man, confirmed Saturday as the yacht's cook, was found shortly afterwards.
A major search operation including specialist divers subsequently identified the bodies of four of Lynch's friends on Wednesday, then Lynch himself on Thursday.
The ship sank by its stern -- the back -- and came to rest on its right side on the sea bed, some 50 metres down, Girolamo Bentivoglio Fiandra of the fire service said.
He said the passengers trapped inside "took refuge to seek safety in the cabins on the left side where somehow the last air bubbles formed".
"We found the first five bodies in the first cabin on the left side, and the last body in the third cabin on the left side," he said.
Bayesian's emergency flare had gone up at 4.38 am (0238 GMT) on Monday morning, and the coastguard immediately deployed -- but when they got there, it had already sunk.
Information on whether the yacht's doors were open -- which might explain why it sank so fast -- would not be possible to confirm until the wreck was recovered, officials said.
This could take weeks.
Lynch, once dubbed the British "Bill Gates", founded software firm Autonomy in the 1990s. Its $11 billion sale to Hewlett-Packard in 2011 saw him face fraud charges in the United States.
A jury in San Francisco acquitted the 59-year-old and a co-defendant of all charges in June.
After Hannah's body was brought ashore on Friday, her family issued a statement describing their "unspeakable grief".
"The Lynch family is devastated, in shock and is being comforted and supported by family and friends," it said.
