The submarine Titan plunged thousands of feet into the North Atlantic Ocean while searching for the wreck site of the Titanic when the ship imploded, killing all five people on board.
Those crouched inside the doomed deep-water vessel, which set sail from the Canadian coast on June 18, 2023, were the American CEO and pilot, a French sailor, two businessmen and one of their sons - the youngest passenger at 19 - who brought his Rubik's Cube along on the journey in hopes of breaking a world record.
What exactly led to the disaster that gripped the world and prompted speculation on social media about the sailors' chances of survival is the subject of a two-week U.S. Coast Guard investigative hearing that began Monday in North Charleston, South Carolina.
Officials said several aspects surrounding the cause of the failure will be investigated, including "historical events prior to the accident, regulatory compliance, crew member duties and qualifications, mechanical and structural systems, emergency response, and the underwater industry."
Among the witnesses scheduled to appear before the Marine Board of Investigation are engineers and executives from OceanGate, the Washington state company that developed and operated the Titan, as well as co-founder Guillermo Söhnlein.
At a news conference on Sunday, Jason Neubauer, chairman of the Marine Board of Investigation, said the purpose of the hearing is to make necessary safety recommendations for federal and international agencies to consider so that "no family ever has to experience such a loss again."
He added that the council will also determine the extent of any negligence or misconduct and that any potential criminal offences will be referred to the Ministry of Justice.
OceanGate came under intense scrutiny following the disaster, a nearly unheard-of event in the submarine industry. (Submarines differ from submarines in that they are typically smaller and require support ships or platforms to launch and recover.)
Experts familiar with the Titan's design have spoken openly about several potential cost-saving factors that may have led to its implosion. Those include the 23,000-pound vessel being made of experimental materials like carbon fiber, which they say has not been pressure-tested over time at such extreme depths, and that the submarine's hull was designed to carry more passengers rather than in the more familiar spherical shape.
On its website at the time, OceanGate touted that the Titan was made of "titanium and filament-wound carbon fiber" and that it had "proven to be a safe and comfortable vessel" that could "withstand the enormous pressures of the deep ocean."
On its website, OceanGate now simply says it has "suspended all exploration and commercial activities."
The Titan lost contact with the Polar Prince, the support ship, nearly two hours into its descent to view the Titanic wreck, which lies at a depth of about 13,000 feet. OceanGate promised travelers a roughly two-and-a-half-hour trip to the site, with another four hours to tour the famous sunken ocean liner before returning.
But after the Titan failed to return at the scheduled time, the Polar Prince contacted the Coast Guard. Wreckage from the Titan was found during a search four days later, and while the public was fascinated by how long the passengers could hold out in a cramped tube without air, officials said they likely died instantly in a "catastrophic implosion" because the vessel couldn't handle the pressure of deep-sea water.
The dead included OceanGate CEO Stockton Rush, 61, who was piloting the Titan; French explorer Paul-Henri Nargeolet, 77, who had experience visiting the Titanic wreck site; British magnate Hamish Harding, 58; and Pakistani businessman Shahzada Dawood, 48, and his teenage son Suleman.
The passengers each paid $250,000 to visit the Titanic wreck, The Associated Press reported.
After the Titan implosion, Söhnlein, the co-founder of OceanGate who left the company in 2013, stressed that Rush was "very committed to safety."
"Stockton was one of the most astute risk managers I have ever met," said Söhnlein, adding: "When I was there, we were always very transparent with everyone who went on expeditions with us about the risks involved."
But others had warned.
Former employee David Lochridge, who was hired to conduct manned submarine tests, alleged in a 2018 counterclaim to OceanGate that he was fired after warning that the Titan's carbon casing had not been properly tested to ensure the ship could sink as far as the Titanic.
Lochridge said in court documents that after he complained that passengers' lives were in danger, he was given "10 minutes to immediately clean up his desk."
OceanGate initially sued Lochridge for breach of contract, but the two sides later settled their dispute. Lochridge is expected to testify at the Coast Guard hearing on Tuesday.
Meanwhile, Nargeolet's estate filed a $50 million wrongful death lawsuit last month, alleging that OceanGate and others involved in its construction were consistently careless, reckless and negligent. The lawsuit is still ongoing, and a former OceanGate engineering executive named as a defendant, Tony Nissen, is expected to appear at the Coast Guard hearing on Monday.
Neubauer, chairman of the Marine Board of Investigation, said Sunday that the investigation is one of the most complex for the Coast Guard because of the nature of the Titan incident and the extreme depths at which it occurred, making collecting evidence difficult.
Peter Girguis, a professor at Harvard University and assistant professor of applied ocean engineering and physics at the Woods Hole Oceanographic Institution, said he hopes the hearing will lead to an "honest conversation about what led to this tragedy," while making clear that OceanGate's Titan is not typical of how members of the underwater industry adhere to best practices for design and safety.
He added that the deep ocean needs further exploration, but there also needs to be a broader conversation about whether activities such as the Titanic tour promoted by OceanGate on the high seas outside US jurisdiction should be regulated.
"We need to support innovators who think outside the box, but we need to make sure they don't cause bodily harm or result in the loss of life of others who are not complicit in this action," Girguis said. "The Titan submarine went down not only with its inventor, but also with paying passengers."
This article was originally published on NBCNews.com