Five experienced Italian divers died in the Maldives last week, with four of them believed to still be deep inside an underwater cave.And in a perilous mission to try to recover their bodies, a military rescue diver also died on the weekend.Now, expert deep-sea divers from Finland have arrived in the archipelago to map out a new plan to retrieve the four divers.It will involve entering the cave about 50 metres below the ocean's surface and searching a labyrinth hundreds of metres long, featuring multiple chambers and narrow passages.Here's what we know about the "highly complex" mission.Five divers die, four remain missingThe five Italian divers were exploring a series of underwater caves about 50m deep in Vaavu Atoll on Thursday when disaster struck.Four of the divers were affiliated with the University of Genoa, including two who were on an official scientific mission to monitor marine environments.The fifth person was the group's diving instructor, Gianluca Benedetti.Benedetti's body was recovered on Thursday near the mouth of a cave, south of Alimatha island, in the eastern Maldives' Vaavu Atoll.Authorities believe the remaining have four died after they entered the cave.Monica Montefalcone (left) and daughter Giorgia Sommacal were among the five divers. (Supplied)A mother and daughter are among the victims: Monica Montefalcone, an associate professor of ecology, and her daughter, Giorgia Sommacal, a biomedical engineering student at the university.Research assistant Muriel Oddenino and Federico Gualtieri, a recent marine ecology master's graduate from the university, are also missing.The University of Genoa has said Sommacal and Gualtieri were not involved in the scientific mission, and that the dive in which the group went missing was "undertaken privately".The divers had been on a week-long trip alongside about 20 other passengers.Muriel Oddenino was one of the five divers who died in the scuba accident in the Maldives. (Supplied: Facebook)Carlo Sommacal, Giorgia's father and husband to Monica, said his wife was "one of the best divers on Earth"."She's probably done 5,000 dives, and she's always been conscientious. She would never have put our daughter's or other children's lives at risk," he told la Repubblica."Something must have happened down there. Maybe one of them got into trouble, maybe the oxygen tanks, I have no idea."In a statement, the university paid tribute to the divers who worked at and attended the university."The sympathy of the entire university community goes out to the families, colleagues and students who shared their human and professional journey," it said.Search suspended after rescue diver diesThe search for the four missing divers was suspended over the weekend after a local military diver also died after trying to reach them.Sergeant Major Mohamed Mahudhee, a member of the Maldives National Defence Force (MNDF), died of underwater decompression sickness after being transferred to a hospital in the capital on Saturday.Maldivian authorities searched for the missing divers over the weekend but have since called off the operation. (Maldives President's Media Division via AP)Search operations had involved eight local divers who worked in shifts to locate the bodies after initial teams identified and marked the entrance.Sergeant Major Mahudhee reportedly searched the first two large chambers of the system and had attempted to reach the third through narrow interconnecting passages.Rough weather has also repeatedly hampered efforts to retrieve the divers' bodies.Finnish divers tasked with 'highly complex' retrievalDiving safety organisation DAN Europe has now sent three expert Finnish divers to the Maldives.The team includes Sami Paakkarinen and Patrik Grönqvist, who gained global renown after the documentary Diving Into The Unknown chronicled their role in the 2014 Plura cave-diving incident in Norway, as well as Jenni Westerlund.DAN Europe chief executive Laura Marroni said the mission involves "highly complex operational characteristics".The divers went missing near an underwater cave south of Alimatha island, located in the eastern Maldives' Vaavu Atoll. (ABC News)"Access to the cave is located at a depth of between 55 and 60 metres, while the underwater system extends for hundreds of metres through multiple chambers and internal passages," she said."The victims may be located in areas that are difficult to access, requiring extremely careful planning of every phase of the intervention."The Maldives government has said it expects the three specialists to reassess the "high risk" recovery operation and determine whether it could continue safely.Dive depth exceeded recreational limit in MaldivesDiving at 50m exceeds the maximum depth recommended for recreational divers by most major established scuba certifying agencies, with depths beyond 40m requiring specialised training and equipment.The recreational diving limit in the Maldives is 30m.Albatros Top Boat, the Italian tour operator managing the Duke of York on which the five Italian scuba divers had been travelling, has denied authorising or knowing about the group's plans to explore caves 50m deep.The Maldives is widely considered one of the world's best diving destinations. (AP)Orietta Stella, representing Albatros Top Boat, has told Italy's Corriere della Sera that the dive far exceeded what was planned for a scientific cruise focused on coral sampling at standard depths.She said the victims were experienced divers, but the equipment they were using appeared to be standard recreational gear rather than technical, deep-diving equipment.Weather warnings of rough seas and strong winds had also been issued on the day of the dive, while the site is known to have strong currents.Shaff Naeem, an advisor to the MNDF who has carried out more than 50 technical dives in the cave, said the divers could have had inadequate gas supplies and been impacted by nitrogen narcosis.Strong currents can also cause sediment clouds that significantly reduce visibility inside deep-sea caves, leaving divers at risk of becoming disoriented.ABC/wires