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Investigators continue to scour the ocean floor for any insight into how a "catastrophic implosion" killed all five passengers of a Titanic-bound submersible that suddenly lost communication with its mother ship last weekend, officials said.
A dayslong international search effort concluded on Thursday after debris from the Titan submersible was found about 480 metres from the historic wreckage of the Titanic.
Military experts found the debris consistent with the disastrous loss of the small vessel's pressure chamber, US Coast Guard Rear Adm. John Mauger announced.
READ MORE: What we know about the 'catastrophic implosion' on Titan sub
The passengers killed were a Pakistani businessman and his son, Shahzada and Suleman Dawood; British businessman Hamish Harding; French diver Paul-Henri Nargeolet; and Stockton Rush, the CEO of the vessel's operator, OceanGate Expeditions.
As officials work to determine the timeline and circumstances of the accident, remotely operated vehicles will be used to map out the Titan's debris field more than 3.2 kilometres deep in the North Atlantic Ocean, Mauger said.
READ MORE: Teen was 'terrified' in lead up to doomed Titanic sub trip
Meantime, Titan's mother ship leaves the search area on Friday and is expected arrive back at port in St. John's, Newfoundland, by early Saturday, a source with Horizon Maritime, the company that owns the ship, told CNN's Miguel Marquez. Marine traffic tracking sites on Friday morning show a line of ships headed back to St. John's.
Officials have yet to conclusively determine whether the devastating implosion occurred at the moment when the submersible stopped communicating about 1 hour and 45 minutes into its dive, Mauger said.
A Navy review of acoustics data detected an "anomaly consistent with an implosion or explosion" on Sunday in the general area the Titan was diving when it went silent, a senior Navy official told CNN.
The information was "immediately shared" with on-scene commanders leading the search and used to narrow the search area, the official said. The sound was determined to be "not definitive" and "the decision was made to continue our mission as a search and rescue and make every effort to save the lives on board."
Once the search began, crews had sonar buoys in the water "nearly continuously" and did not detect any "catastrophic events", Mauger said.
Asked whether any remains may be recovered, Mauger noted the "incredibly unforgiving environment," adding, "I don't have an answer for prospects at this time." A medical expert said a deep-sea implosion would leave behind no recoverable remains.
"There would be virtually nothing," Dr. Aileen Marty, a disaster medicine expert at Florida International University, told CNN's Anderson Cooper. "They're very unlikely to find anything there of human tissue."
OceanGate touted its dives as a "truly extraordinary" once-in-a-lifetime experience amid a growing industry of adventure tourism for the ultra-wealthy. A seat on a Titanic expedition cost each passenger $US250,000 ($374,000), an archived version of OceanGate's website shows.
But the tragedy has renewed scrutiny of OceanGate's operations and the development of the 6.4 metres, 10-tonne Titan craft amid mounting reports of safety concerns, mechanical problems and an alleged disregard for regulatory processes.
OceanGate co-founder Guillermo Sohnlein said the deaths are a "tragic loss for the families and for the ocean exploration community in general" and noted the inherent risk in such trips.
"Those of us in the community that work at that depth know that that's always a risk," Sohnlein told CNN on Thursday. "There's pressure down so intense that if there is a failure, it is an instant, catastrophic failure."
OceanGate co-founder defends sub deployment
As OceanGate faces questions about its operations and safety practices in the wake of the Titan's fatal implosion, Sohnlein also defended the company's approach to designing and deploying the vessel.
Sohnlein had "complete faith" in co-founder Rush, who had previously expressed skepticism of regulations that might slow innovation, he said.
"I've broken some rules to make this," Rush told travel blogger Alan Estrada of the Titan in 2021.
Rush was not a "risk taker," he was a "risk manager," Sohnlein said.
"We won't know anything until the investigation is complete and all the data is collected, so I'll reserve judgment," Sohnlein said. "But I've known him for 15 years, and none of this would change my mind."
"There are teams on site that are still going to be collecting data for the next few days, weeks, maybe months, and it's going to be a long time before we know exactly what happened down there," Sohnlein said on Friday morning. "I would encourage us to hold off on speculation until we have more data to go on."
At least two former OceanGate employees voiced safety concerns about the development of the vessel's hull years ago, including about testing procedures and the thickness of its carbon fibre frame, CNN has reported.
Additionally, uncertainty after a 2021 Titan test dive led Discovery Channel's Expedition Unknown host Josh Gates and his team to decide not to film a segment on the vessel as it "became clear to us at that time that there was a lot that needed to be worked out with the sub," he said.
"A lot of the systems worked, but a lot of them really didn't. We had issues with thrusters and issues with computer control and things like that," Gates said. "Ultimately, it was a challenging dive."
The company has also grappled with a series of mechanical problems and inclement weather conditions that forced the cancellation or delays of trips in recent years, according to court records.
The difficulties led to a pair of lawsuits in which some high-paying customers sought to recoup the cost of excursions they said they didn't take and alleged the company overstated its ability to reach the Titanic wreckage.
OceanGate did not respond to the claims in court and could not be reached for comment.
Loved ones mourned as intrepid adventurers
In addition to Rush, who was piloting the Titan expedition, the victims include two veteran explorers and a father-son duo from a prominent Pakistani business family.
Acclaimed French diver Paul-Henri Nargeolet was accompanying the mission as a content expert intimately familiar with the Titanic wreckage, according to OceanGate's archived website.
Nargeolet served as the director of underwater research at RMS Titanic Inc., the company that holds exclusive rights to salvage artefacts from the ship. He had performed 35 dives to the wreck and oversaw the recovery of 5000 artefacts, according to his biography on the company's website.
The diver's family remembered him as a beloved father and husband who "will be remembered as one of the greatest deep-sea explorers in modern history."
"But what we will remember him most for is his big heart, his incredible sense of humour and how much he loved his family. We will miss him today and every day for the rest of our lives," his wife and children said in a statement on Thursday.
Hamish Harding, a British businessman with a remarkable resume of extreme expeditions, has participated in several record-breaking trips. He was a member of a 2019 flight crew that broke the world record for the fastest circumnavigation of the globe via both poles and in 2020 became one of the first people to dive to Challenger Deep in the Pacific Ocean, widely believed to be the deepest point in the world's oceans.
The globetrotter owned the aircraft brokerage Action Aviation and was beloved by his wife and two sons, his family said in a statement.
"He was a passionate explorer – whatever the terrain – who lived his life for his family, his business and for the next adventure," the statement said. "What he achieved in his lifetime was truly remarkable and if we can take any small consolation from this tragedy, it's that we lost him doing what he loved."
Pakistani billionaire Shahzada Dawood and his son Suleman were also on the Titan. Their family's business, Dawood Hercules Corp., is one of Pakistan's largest corporations.
"Please continue to keep the departed souls and our family in your prayers during this difficult period of mourning," family patriarch Hussain Dawood and his wife Kulsum said in a statement on Thursday.
Shahzada Dawood was intelligent and perpetually curious, his friend Bill Diamond told CNN on Wednesday. He didn't think of Dawood as an adventurist but believes he was aware of the Titan trip's risks, Diamond said.
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