US and Canada start the process of determining how the Titanic-bound submersible imploded

Authorities from the U.S. and Canada began the process of investigating the cause of the fatal Titan submersible implosion even as they grappled with questions of who was responsible for determining how the tragedy unfolded.

A formal inquiry has not yet been launched because maritime agencies are still busy searching the area where the vessel was destroyed, killing all five people aboard, the U.S. Coast Guard said Friday. Debris was located about 12,500 feet (3,810 meters) underwater, several hundred feet away from the Titanic wreckage it was on its way to explore.

The U.S. Coast Guard led the initial search and rescue mission, which was a massive international effort that likely cost millions of dollars.

It was not entirely clear Friday who would have the authority to lead what is sure to be a complex investigation involving several countries. OceanGate Expeditions, the company that owned and operated the Titan, is based in the U.S. but the submersible was registered in the Bahamas. OceanGate is based in Everett, Washington, but closed when the Titan was found. Meanwhile, the Titan’s mother ship, the Polar Prince, was from Canada, and those killed were from England, Pakistan, France, and the U.S.

The National Transportation Safety Board said Friday that the U.S. Coast Guard has declared the loss of the Titan submersible to be a “major marine casualty” and the Coast Guard will lead the investigation. NTSB spokesperson Peter Knudson said that information was provided to the agency’s senior management by Coast Guard officials, and the NTSB has joined the investigation.

The Coast Guard has not confirmed that it will take the lead. Coast Guard headquarters said the Coast Guard First District in Boston will discuss future operations and plans, but did not say when. The First District did not respond to phone and email messages seeking comment Friday.

Meanwhile, the Transportation Safety Board of Canada said Friday that it is launching an investigation into the Polar Prince. Seventeen crew members and 24 others were on board the ship during the Titan's journey.

The deep-sea investigations promise to be long and painstaking, as is the nature of investigations in the murky depths of the ocean.

“This is an incredibly unforgiving environment down there on the seafloor,” said Rear Adm. John Mauger, of the Coast Guard First District.

How the overall investigation will proceed is complicated by the fact that the world of deep-sea exploration is not well-regulated. Deep-sea expeditions like those offered by OceanGate are scrutinized less than the companies that launch people into space, noted Salvatore Mercogliano, a history professor at Campbell University in North Carolina who focuses on maritime history and policy.

A key part of any investigation is likely to be the Titan itself. Questions have been raised about whether the vessel was destined for disaster because of its unconventional design and its creator’s refusal to submit to independent checks that are standard in the industry

The Titan was not registered as a U.S. vessel or with international agencies that regulate safety. And it wasn't classified by a maritime industry group that sets standards on matters such as hull construction.

OceanGate CEO Stockton Rush, who was piloting the Titan when it imploded, complained that regulations can stifle progress.

“Bringing an outside entity up to speed on every innovation before it is put into real-world testing is anathema to rapid innovation,” Rush wrote in a blog post on his company’s website.

One question that seems at least partially resolved is when the implosion likely happened. After the Titan was reported missing, the Navy went back and analyzed its acoustic data and found an “anomaly” Sunday that was consistent with an implosion or explosion in the general vicinity of where the vessel was operating when communications were lost, said a senior U.S. Navy official.

The Navy passed on the information to the Coast Guard, which continued its search because the data was not considered definitive, according to the official, who spoke on condition of anonymity to discuss a sensitive acoustic detection system.

The Titan launched at 8 a.m. that day and was reported overdue that afternoon about 435 miles (700 kilometers) south of St. John’s, Newfoundland. Rescuers rushed ships, planes and other equipment to the area.

Any sliver of hope that remained for finding the crew alive was wiped away early Thursday, when the Coast Guard announced that debris had been found near the Titanic.

Killed in the implosion were Rush, two members of a prominent Pakistani family, Shahzada Dawood and his son Suleman Dawood; British adventurer Hamish Harding; and Titanic expert Paul-Henri Nargeolet.

A flurry of lawsuits is expected, but filing them will be complex and it's unclear how successful they will be. Plaintiffs will run into the problem of establishing jurisdiction, which could be tricky, just as it will be for the investigation, said Steve Flynn, a retired Coast Guard officer and director of Northeastern University’s Global Resilience Institute.

The implosion happened “basically in a regulatory no man’s land,” Flynn said.

“There was essentially no oversight,” Flynn said.

James Cameron, who directed the blockbuster movie “Titanic” and has made multiple dives to the iconic ship's wreckage, told the BBC that he knew an “extreme catastrophic event” had happened as soon as he heard the submersible had lost navigation and communications at the same time.

“For me, there was no doubt," Cameron said. "There was no search. When they finally got an ROV (remotely operated vehicle) down there that could make the depth, they found it within hours. Probably within minutes.”

At least 46 people successfully traveled on OceanGate’s submersible to the Titanic wreck site in 2021 and 2022, according to letters the company filed with a U.S. District Court in Norfolk, Virginia, that oversees matters involving the Titanic shipwreck.

But questions about the submersible's safety were raised by both by a former company employee and former passengers.

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Associated Press writers Lolita C. Baldor in Washington; Ben Finley in Norfolk, Virginia; Holly Ramer in Concord, New Hampshire; David Sharp, in Portland, Maine; and Gene Johnson in Seattle contributed to this report.