Prosecutors in Italy have launched an official investigation into the captain of the £30million Bayesian superyacht which sank off Sicily last week, killing British tech billionaire Mike Lynch, his daughter and five others. 

Captain James Cutfield, a 51-year-old New Zealander, is being investigated for manslaughter and shipwreck, Italian dailies La Repubblica and Corriere della Sera are reporting today.

Being placed under investigation in Italy does not imply guilt and does not mean formal charges will necessarily follow.

Six passengers - including Mr Lynch and his 18-year-old daughter Hannah - died alongside chef Recaldo Thomas after the British-flagged pleasure yacht capsized and came to rest on its side 164ft below in the early hours of last Monday.

Hundreds of people in the Sicilian fishing community of Porticello, held a poignant candle-lit vigil for the victims last night, as a former marine who guarded Mr Lynch while he was under house arrest said the experience was 'life-changing'. 

A weather phenomenon known as a downburst - a violent downward explosion of wind that then expands outwards as it hits the ground, often produced in thunderstorms and mistaken for tornadoes - is believed to have played a part. 

While the yacht had been hit by the very sudden meteorological event, it was plausible that crimes of multiple manslaughter and causing a shipwreck through negligence had been committed, chief prosecutor of Termini Imerese, Ambrogio Cartosio, said on Saturday.

Maritime law gives a captain full responsibility for the ship and the crew, as well as the safety of all aboard.

Prosecutors in Italy have previously questioned Cutfield, who they said had been 'extremely cooperative'. Other Bayesian crew members have remained in Italy voluntarily to assist the investigation.

It comes after Italian prosecutors held a press conference on Saturday, where it was revealed the victims were unable to escape as they may have been asleep.

They had scrambled to one side of the ship in search of air pockets in a desperate attempt for survival, with Hannah - who had won a place at the University of Oxford - dying alone in a cabin.

At the Termini Imerese Courthouse in Palermo, Mr Cartosio did not rule out homicide charges.

One line of inquiry being pursued by prosecutors is whether the nine surviving crew members raised the alarm before escaping.

Mr Cartosio vowed to establish each crew members' responsibility as he warned: 'For me, it is probable that offences were committed - that it could be a case of manslaughter.'

He said there were 'behaviours that were not perfectly in order with regard to the responsibility everybody had', before adding: 'There could be in fact the question of homicide. But this is the beginning of the inquiry, we cannot exclude anything at all.'

A vigil for the victims of the disaster was held last night in the fishing community of Porticello in Sicily. 

It comes as tributes continued to pour in for the victims, with the security guard who ensured Mike Lynch remained under house arrest during his trial in America revealing the mogul treated him like a member of his family.

Rolo Igno, a court-appointed armed guard, said: 'As an executive protection agent, the number one rule is simple, don't ever get close to the principal. 

'They aren't your friends, they're a client and the relationship is strictly professional. But with Mike, that didn't fly with him and for me that rule quickly dissolved.'

Describing the first time he escorted Dr Lynch and his daughters to lunch, he said: 'I opened the door for them and told Mike, ''If you need anything at all sir, I'll be right at this table by the entrance''. He chuckled and in his confident way, Mike replied, ''No, no, no, you'll be sitting with us''.

'When I hesitated, not wanting to disrupt their family time, he insisted, saying, 'Rolo, do you want me to tell my beautiful daughters that the tough and handsome security guy, who was a former marine, didn't want to sit with us because he was intimidated by them?' How could I possibly say no to that?

'So, I joined them, sitting at the far end of the table, feeling out of my element but gradually realising how genuine and loving they all were.'

The victims' bodies were tragically found in 'tight spots' with furniture on top of them and brought ashore one-by-one by dive teams last week, who had carried out 120 trips to the wreck on the seabed.

Fifteen of the 22 people on board the ship - including Hannah's mother Angela Bacares, 57 - managed to escape in a liferaft.

Italian prosecutors have admitted they did not conduct alcohol and drug testing on the vessel's crew - all but one of whom survived - because they needed treatment and were in shock. They have vowed to question the sailors intensively.

The coastguard says no tornado warning had been issued that night, contrary to previous reports, and the ship's captain Mr Cutfield reportedly told Italian newspaper La Repubblica of the sudden weather change: 'We didn't see it coming.'

Mr Cartosio previously said he thought it was 'probable that offences were committed' surrounding the sinking of the yacht. 

He opened a case of shipwreck and manslaughter that was not initially directed at any individuals. Mr Cutfield is now being investigated for shipwreck and manslaughter.

According to a live translation provided by the BBC, Mr Carosio told reporters that the sinking could have been the responsibility of the captain, crew, individuals in charge of supervision, the ship-builder, or others.

He added: 'We will establish each element's responsibility - that will be done by the inquiry, so we can't do that prematurely.

'For me, it is probable that offences were committed - that it could be a case of manslaughter - but we can only establish that if you give us the time to investigate.

'Media timing is completely different from that of a prosecutor. We need a minimum amount of time to come to a proper scientific conclusion.'

Mr Cartosio, while stressing that enquiries remain at an early stage, appeared to suggest there were questions for the crew to answer.

He added that it would be 'painful' if, theoretically, 'this tragedy, this terrible tragedy, was caused by behaviours that were not perfectly in order with regard to the responsibility that everybody had to have (on) the ship.' 

He added: 'Individuals or people would potentially be culpable, negligent, lack of prudence, lack of responsibility... We can't just deal with this quickly.'

Lead prosecutor Raffaele Cammarano added of the crew: 'We are going to discover how much they knew or to what extent all the people were warned.

'This event was completely unexpected so the inquiry which as the prosecutor previously said is going to be based on recovery of the wreck, when we'll be able to examine the wreck and possibly get some answers to questions that at the moment cannot be answered.' 

The disaster killed six passengers and one member of crew. Among the survivors are six other passengers and nine members of the crew, including Mr Cutfield, and the first officer.

Questions remain as to whether those who died had been warned the boat was in trouble - and how long it took for the Bayesian to sink while the 15 survivors were rescued after a passing ship sent out a lifeboat.

Stephen Askins, a partner at maritime law specialists Tatham & Co, previously told MailOnline the forecasted bad weather likely meant the crew were already up and working when the Bayesian sunk, allowing them to quickly escape in a liferaft.

The time it took the boat to sink, combined with the actions of the crew as it became apparent it was in trouble, will likely form the core of any manslaughter inquiry. 

The yacht is believed to have sunk at the stern after being upset by a downburst that spread out with force, coming to rest on its right-hand side as it hit the sea bed.

Rescue chiefs said it was apparent to divers that victims had tried to seek shelter in one side of the upturned boat, where there may have been air bubbles, as it sank.

Hannah was found alone in her cabin while five others, including her father, were found in a separate compartment. 

Fire service commander Girolamo Bentivoglio Fiandra told reporters at a conference in Termini Imerese, close to the sinking site at Palermo: 'You may want to know where we recovered the bodies of the victims. I can tell you... that the ship sunk and was laid onto its right hand side at the bottom of the sea. 

'It's quite clear that the people were trying to hide in the cabins on the left-hand side and we found the first five bodies in the first cabin on the left-hand side and the final body in the third cabin on the left-hand side.

'There were six cabins: three on the left-hand side and three on the right-hand side. We found them on the highest part of the ship going towards the surface.'

One person had been on watch in the cockpit when disaster struck. They have been interviewed and are not required to remain in Italy - but authorities say they expect them to fully cooperate with the probe.

Prosecutors say they want the Bayesian to be raised from the water so the wreck can be examined but responsibility for this lies with the ship's owners. 

The 185ft British-flagged yacht sank in the early hours of Monday after, investigators believe, it was struck by a downburst, a violent downward plume of wind often mistaken for tornadoes and commonly created during thunderstorms.

The emergency services were alerted shortly after 4.30am - but by the time they had arrived, the ship had already sunk. 

The time taken by rescue services to reach the wreck will also form part of the investigation - though authorities said today the sinking had been extremely rapid.

The crew of a nearby Dutch sailing ship, the Sir Robert Baden Powell, were able to send a liferaft to rescue 15 of the 22 people on board. Among the survivors was British woman Charlotte Golunski and her one-year-old daughter, who she held aloft in the water.

Mr Cartosio added that it quickly became apparent to those who witnessed the disaster it would be 'impossible' to save those still trapped in the yacht as it sank to the sea bed.

He told reporters: '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.'

He added: 'Generally a prosecutor is never satisfied to give this information at this stage, precisely because developments could change. 

'We cannot exclude anything at all but what, there has been a lot of media interest with regards to the people who were involved. But at the same time I believe it is right to anticipate developments of this inquiry can be very variable.' 

There had been questions as to why it had taken so long for Italian authorities to inform the public in detail of its rescue operations.

Mr Cartosio told reporters Italian civil codes had prevented him from releasing more information about the search while it took place, highlighting that he personally believed it created 'notable obstacles' to transparency with the public.

However, the press conference was staged because of the major international interest in the disaster - and because of the high-profile identities of the victims.  

Mr Lynch and his daughter, alongside Morgan Stanley International bank chairman Jonathan Bloomer, his wife Judy Bloomer, Clifford Chance lawyer Chris Morvillo and his wife Neda Morvillo were lost when the yacht sank at around 5am local time on Monday.

The body of Canadian-Antiguan national Recaldo Thomas, who was working as a chef on the superyacht, was recovered at the scene of the sinking on Monday. 

Their bodies were taken to the nearby village of Porticello, about 11 miles from Sicilian capital Palermo. 

Rear Admiral Raffaele Macauda, maritime director of western Sicily confirmed Thomas' body was found close to the ship.

Mr Fiandra, the fire service commander, added that it had taken time to find the other bodies because of the complexities of reaching a ship 50 metres below, the size of the yacht itself, and the lack of visibility so far from the surface.

'Over four days to have obtained the result we have obtained? Let's say that represents how professional these divers were,' he said.

There is no timeline for when the yacht may be recovered from the water to assist with the ongoing investigation. 

'We want to be able to recover the wreck in coordination with the prosecutor because there will be inquiries and they have shown the will to recover the wreck,' Rear Admiral Macauda said. 

'We carried out an extraordinary operation and everyone worked in an amazing way. But this is a very sad moment as seven human lives have been lost.'

He later added: 'What of course we wanted to do is save human lives at sea. That's why we carried on with the search from the surface. We were still hoping to find somebody alive.'

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.

A total of 27 divers, including 11 cave experts and eight deep sea divers, were called in to aid with the search across 72 total hours of searching underwater across 123 dives. 

In a statement, the family of Mr Lynch and Hannah said: '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.

'They would like to sincerely thank the Italian coastguard, emergency services and all those who helped in the rescue.

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

The Lynch family also issued a photograph of Mr Lynch and Hannah alongside their tribute.

Hannah's sister Esme paid her own tribute, saying: 'Hannah often burst into my bedroom and lay down with me.

'Sometimes beaming with a smile, sometimes cheeky, sometimes for advice.

'No matter what, she brought boundless love to me.

'She was endlessly caring, passionately mad, unintentionally hilarious and the most amazing, supportive and joyful sister and best friend to me.

'And on top of all this, she had even more love to give endlessly to all her friends and passion to give to her incredible studies and goals.

'She is my little angel, my star.'

Vincenzo Zagarola, of the Italian Coastguard, said the search for Hannah was not 'easy or quick', comparing the sunken yacht to an '18-storey building full of water'.

The bodies of all six missing passengers have now been brought to shore in the small fishing village of Porticello, around 11 miles from the Sicilian capital of Palermo.

Of the 22 passengers and crew on board, 15, including Mr Lynch's wife, Angela Bacares, were rescued after escaping on to a lifeboat. She owns the yacht through a private company.

The boat trip was a celebration of Mr Lynch's acquittal in a fraud case in the US.

The businessman, who founded software giant Autonomy in 1996, was cleared in June of carrying out a massive fraud relating to its 11 billion dollar (£8.64 billion) sale to US company Hewlett Packard.

The Mail reported last night that Hewlett Packard has refused to rule out pursuing Mr Lynch's family over a legal case. 

His death last week means his family could be liable for any payout decided by the judge, who is expected to rule on damages before the end of the year.

A source close to the case said: 'It is with the judge. We are waiting to hear from him. There is no decision to be made until he makes his decision.' A spokesman for Hewlett-Packard Enterprise, asked if it would rule out pursuing Dr Lynch's estate for damages, said: 'We do not think it appropriate to comment on legal matters in these tragic circumstances.'