A local expert who has dived in caves in the Maldives 'countless times' has described the terrifying final moments a group of five divers may have endured - and dubbed the tragedy an accident waiting to happen. 

Alarm bells were raised on Thursday after five Italians, including a mother and daughter, failed to resurface after attempting to explore the caves at a depth of around 165ft [50m].

The body of the local instructor who led the group, Gianluca Benedetti, was discovered within the passageway from the mouth of the Thinwana Kandu cave, also known as Shark Cave, on Friday, at a depth of around 197ft [60m].

The rest of the group was found on Monday by the team of three Finnish divers trapped at the end of the tunnel, deep at the bottom of the cave's third chamber, which is in complete darkness.

This now marks one of the worst single diving accidents in the history of the Indian Ocean nation. 

'I have visited those caves countless times. There is no current. They swam into that third cave. They chose to go in there,' Shafraz Naeem, a former military diver for the Maldives National Defence Force, told the Daily Mail.

'I believe the instructor intentionally swam away from the group. Maybe he legged it up before he ran out of air. The rest of the group died in that third chamber and Benedetti died in the passageway trying to get out.'

The cave is divided into three separate chambers, connected by narrow passageways, which sharks, stingrays and lobsters inhabit. Mr Naeem, despite being an expert diver, has intentionally never entered the third chamber due to safety concerns.

The cave opens at 164ft (50m), which is already significantly deeper than the 98ft (30m) recreational diving limit under regulations in the Maldives. The Indian Ocean nation is known as a diving location that strictly regulates technical diving, making it near impossible to do while restricting available equipment. 

'The cave is unforgiving,' Mr Naeem, who is from the island of Male, described. 'It is closed, pitch-black and you can only see where you shine the light. 

'If something goes wrong, you cannot shoot up to the surface like you can in open dives. You are stopped and restricted, and, at that depth of below 55m [181ft], it is just completely dangerous.'

The perilous conditions initially limited the search for the group, notably conducted by professional divers, due to considerations over oxygen and decompression - as well as rough weather and sea conditions.  

An initial search operation for the victims ended in tragedy on Saturday when Maldivian military rescue diver Mohamed Mahudhee was admitted to hospital and died from decompression sickness after assisting in the recovery effort. 

Mr Mahudhee was a close friend of Mr Naeem. The 50-year-old is now questioning why the Maldivian government made the decision to send his pal down as an emergency diver who 'doesn't have the proper training and equipment', given the nation's restrictions on technical dives - adding: 'Maybe a politician wanted a badge.' 

As well as Benedetti, the other victims of the diving group have been identified as Monica Montefalcone, an associate professor of ecology at the University of Genoa; her daughter, Giorgia Sommacal; marine biologist Federico Gualtieri and researcher Muriel Oddenino.

Notably some members of the group seemingly did not have adequate diving qualifications for the caves depth, Mr Naeem said, nor where well-known safety rules followed.

The use of ropes, or lines known as 'Ariadne's thread', is mandatory in certain caves to guide divers and keep them together, especially in darkness or at extreme depths. 

However no ropes were found within the cave walls when the trapped bodies were recovered, Mr Naeem said, further implying the group's ill-preparation. 

Despite visiting the caves numerous times and recovering drowned bodies as a previous profession, the military diver has never traced the groups journey into the third chamber - and believes last week's tragedy was 'an accident waiting to happen', with a lack of knowledge and prior groundwork.

He added: 'The talk on the local island is they must have tried to plan it, otherwise they wouldn't have done it.'

For a dive of this depth, technical diving equipment is required, while the group was discovered carrying only recreational gear, used to dive down to 98ft [30m].

Mr Naeem explained: 'The body of the guide who was recovered had a single air tank on him. Where is your back up or redundancy? People who are not trained in cave diving or without proper equipment, like this, tend to get knocked by nitrogen narcosis. Then things start to spiral down from there and get worse.'

Nitrogen narcosis is the poisoning of blood due to a lack of oxygen, leaving divers with impaired judgement or anxiety. Normal compressed air can become toxic around 181ft (55m) and hits people differently at different depths, dependent on fitness level. 

Mr Naeem speculates the group got into difficulty while in the dark depths and, without ropes to guide them back or the appropriate equipment, ran out of oxygen, were hit by nitrogen narcosis - or the above mixed together.

It is understood the tour operator Albatros Top Boats is known locally for hosting deep dives on its two boats, breaking the government's diving regulations, as officials fail to check up on rule abidance by local companies.

'That operator are well known to do all these deep dives, breaking rules, everybody knows it but don't do anything,' Mr Naeem said. 

'The owner doesn't dive herself but the boat managers are known to go deep, breaking the 98ft [30m] regulations.' 

This is backdropped by the Maldives being the only dive destination in the world where technical diving is banned, therefore the equipment is not readily available to use. 

Current diving regulations date back to 1991, with a current reform being pushed through government to increase recreational dive limits from 98ft  [30m] to 131ft [40m]. 

'Local dive centres and other companies are appeasing tourists and allowing them to dive deeper, where there may be more sharks,' Mr Naeem said. 

'So for them, it is "let's go see the sharks. Let's go see the treasure sharks". A lot of boats go below the legal 98ft, many going to 131ft or 164ft. But this one was life-threatening.' 

The Italian tour operator that managed the diving trip has denied authorising or being aware of the deep dive that violated local limits, its lawyer told Italian daily Corriere della Sera on Saturday.

Orietta Stella, representing Albatros Top Boat, said the operator 'did not know' the group planned to descend beyond 98ft – the recreational diving limit in the Maldives.

That threshold requires special permission from Maldivian maritime authorities, and the tour operator 'would have never allowed it', she said.

The dive far exceeded what was planned for a scientific cruise focused on coral sampling at standard depths, Ms Stella added.

The victims were experienced divers, she said, but the equipment used appeared to be standard recreational gear rather than technical equipment suited for deep cave excursions.

The Divers’ Alert Network Europe (DAN), which deployed the three Finnish divers, said on its website that they are technical and cave divers with international experience in search and recovery missions, including operations in 'deep overhead environments, confined spaces, and high-risk scenarios'.

The team used advanced technical systems, including closed-circuit rebreathers, a system that recycles exhaled breathing gas and removes carbon dioxide through a chemical scrubber, allowing for 'significantly longer dives,' the organisation explained.

Monday's operation involved a 'technical cave dive', beginning at 8.30am Italian time and lasting approximately three hours.

'During this first operational intervention, the team of specialists successfully explored the underwater cave system, assessed the environmenal and operational conditions, located all four victims still missing, and collected the key information needed to plan the next phases of the operation,' said DAN Europe, the organisation responsible for the recovery effort.

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 50m 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 50m 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.'

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

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

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.

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