A man whose marine biologist wife perished during a diving expedition in the Maldives fears 'something must have happened down there' as mystery surrounds the five divers' deaths.

The group, from Italy, had set off on a diving expedition on Thursday morning to explore the Vaavu atoll but never resurfaced.

The decision to try and reach the cave has been questioned by experts, with three key elements raised:

Firstly, a weather warning was in place. High winds whip up waves which in turn could dislodge sand and dirt, obscuring visibility.

Secondly, tourists are not meant to dive below 30 metres. The cave is around 60 metres below the surface.

And finally, the cave itself is notoriously difficult to reach. Maldives government spokesman Mohamed Hussain Shareef said that the cave 'is so deep that even divers with the best equipment do not try to approach'.

'There will be a separate investigation into how these divers went below the permitted depth, but our focus right now is on the search and rescue,' he added.

One of the victims is 51-year-old Monica Montefalcone, a respected marine biologist, TV personality, and professor of Tropical Marine Ecology and Underwater Science at the University of Genoa. Her 22-year-old daughter, Giorgia Sommacal, also died.

Carlo Sommacal, Montefalcone's husband and Giorgia's father, broke his silence following their deaths. 

Devastated Sommacal insisted that 'my wife is among the best divers on earth,' and said she wouldn't have put anyone in the group in danger.

 'She would never have put our daughter's life or that of others at risk... something must have happened down there,' he said. 

'Maybe one of them had trouble, maybe the oxygen tanks, I have no idea.'

The three other victims have been named as Muriel Oddenino of Turin, Gianluca Benedetti of Padua, and Federico Gualtieri from Omegna. 

The group had boarded the 'luxury' Duke of York yacht, a foreign-operated live-aboard diving vessel, and they disappeared near Alimatha, one of the atoll's most popular diving spots. 

The five divers were believed to have been exploring caves at a depth of 164ft when they went missing.

'The weather is not ideal for diving, and we are facing very rough seas. We have deployed our largest Coast Guard vessel to the area, and Italian diplomats are also on site,' government spokesman Shareef added.

Maldivian authorities launched a major rescue operation after the incident on Thursday, deploying boats, aircraft and dive teams to search the area.

Rescuers recovered one body from about 200 feet below the surface on Thursday, and a first round of searches failed to locate the remaining four divers, who were thought to be inside the same cave.

According to reports, the first body recovered yesterday in the Maldives after the tragic dive by Italian divers was that of Gianluca Benedetti. 

Search teams embarked on a second dive on Friday, to no avail. 

Italy's ambassador was on a search vessel, and the Maldives may seek international assistance if needed.

The search for the remaining four bodies will now resume on Saturday. 

The Italian Ambassador to Sri Lanka, Damiano Francovigh, told broadcaster SkyTg24: 'The Maldivian Coast Guard conducted a dive, and entered this cave, which they tell me is 62 meters deep.'

Francovigh, who also has responsibility for the Maldives and has flown to its capital, Malé, added: 'It's a particularly complex dive because the cave is divided into three separate, interconnected segments. '

'On this occasion, the Maldivian divers were only able to enter the first two, then had to come up to allow time for decompression, and have not yet been able to spot the bodies of the other Italian divers. 

'They plan to make another dive, but only tomorrow. 

'The weather conditions in the Maldives are currently very poor, with strong gusts of wind and heavy rain. 

'They also reported strong currents, all of which unfortunately make operations more difficult.'

Conditions were described as unfavourable at the time, with a yellow weather alert in effect for passenger boats and fishermen.

Meanwhile, police have launched an investigation into the tragedy, but the cause of death remains unknown at this time.

Authorities have not ruled out several scenarios, with police probing whether bad weather may have affected the divers' visibility.

According to Italian news outlet La Repubblica, the fact that none of the five divers managed to resurface suggests the group may have become lost within an underwater cave.

With little light and poor visibility due to bad weather, they may have lost their bearings, panicked, and perhaps run out of air while trying to find their way out.

Police also haven't ruled out the possibility that one of the five may have become stuck while the others ran out of air or panicked while trying to free their colleague.

Diving experts have also been speculating on various hypotheses.

According to local media, one of the most widely accepted hypotheses by the coast guard and experts is oxygen toxicity. This phenomenon occurs if the tank's mixture is inadequate, making oxygen toxic at certain depths.

'At 50 meters of depth in the sea, there are several risks; it's a real tragedy,' says Alfonso Bolognini, president of the Italian Society of Underwater and Hyperbaric Medicine.

'There are several hypotheses we can make right now: an inadequate breathing mix can create a hyperoxic crisis when there's an increase in the partial pressure of oxygen in the tissues and blood plasma, which can cause neurological problems.

'Inside a cave at 50 meters of depth, all it takes is a problem for a diver or a panic attack for a diver,' he adds, saying that 'the agitation causes the water to become cloudy and can impair visibility.

'In these cases, the panic component could lead to even fatal errors.'

The yacht company for the Duke of York, as stated on its official website, provides nitrox - the breathing mixture for scuba diving, composed of nitrogen and oxygen.

It is also unclear whether the Italians' dive, being at a depth of over 160ft, was regulated, according to the Maldives National Defence Force.

Meanwhile, it has been revealed that there was no local guide to accompany the group into the cave, as required by Maldivian law.

Investigators are also trying to determine whether the group used an 'Ariadne's thread' - a rope used by divers while exploring caves to help them stay close together and find the entrance and exit to the cavities.

The use of the rope is mandatory in certain caves.

In Italy, the tragedy has sent shockwaves through the academic world.

Milan-born Montefalcone worked at Distav, the Department of Earth Sciences. In the Maldives, she was the scientific director of the island monitoring campaign.

Her department has described her as 'the most experienced, the best, the most competent.'

Montefalcone survived the 2004 Boxing Day tsunami when it struck the Maldives.

Her daughter Giorgia had inherited her mother's passion for sea life and diving, having completed a degree in biomedical engineering at the University of Genoa.

Oddenino, a 31-year-old marine biologist and ecologist, was Montefalcone's colleague.

She was an experienced diver and authored scientific publications. She was described by a loved one as 'sweet and sensitive'.

Benedetti, 44, was an operations manager, a diving instructor and a boat captain.

After working in banking and finance for several years, he turned his passion for diving into a full-time career and moved to the Maldives in 2017.

He was the operations manager and skipper aboard the Duke of York, the diving yacht that the group used for their expedition.

He was described by Albatros Top Boat, the Duke of York's operator, as 'energetic, extremely sporty, and a lover of reading, classic cinema, and chess.'

Speaking about her son's tragic death, Benedetti's mother told Italian news outlet Gazzettino: 'I heard the news from the embassy. I can't say anything, and you can only imagine the pain.'

Gualtieri, 31, was a scuba diving instructor and had recently graduated from the University of Genoa with a degree in marine biology and ecology.

He had previously praised his professor, Montefalcone, saying: 'Ever since I met her, she has always been my guide, encouraging me to follow my dreams and passions.'

His girlfriend, Noemi De Luca, paid a tribute to him on social media, saying: 'Three years together, but always and forever in each other's hearts. You'll always be in my heart.'

She added: 'Just know that I was, am and always will be proud of you.'

Local officials said it was the worst single diving accident in the nation.

Maldives Minister of Tourism Mohamed Ameen said coast guard officers and security forces were scouring remote seas around where the divers were reported missing on Thursday afternoon.

'I am deeply saddened by the tragic deep diving accident in Vaavu Atoll today,' Ameen said in a statement.

'The coastguard and all relevant authorities are actively engaged in the search and recovery operation.'

The Duke of York's operator declined to comment when approached for comment.

Rome's prosecutor's office has opened an investigation into the death of the five Italians.

The Maldives, a nation of 1,192 tiny coral islands scattered some 500 miles across the equator in the Indian Ocean, is a luxury holiday destination popular with divers, who often stay at secluded resorts or on dive boats.

Local regulations allow dives to a maximum depth of 98 feet, but experienced professionals are known to go deeper.

Diving and water-sport-related accidents are relatively rare in the South Asian nation, although several fatal incidents have been reported in recent years.

A British woman tourist died while diving in December, and her distraught 71-year-old husband died a few days later after falling ill.

A 26-year-old Japanese tourist went missing after a diving expedition near the capital in June.

Local media reported last year that at least 112 tourists had died in marine-related incidents in the archipelago over the previous five years, including 42 in diving or snorkelling accidents.