In this satellite image provided by Maxar Technologies, from top to bottom, the vessels Horizon Arctic, Deep Energy and Skandi Vinland search for the missing submersible Titan, Thursday, June 22, 2023 in the Atlantic Ocean. (Satellite image ©2023 Maxar Technologies via AP)

The around-the-clock search for the missing Titan submersible engrossed the world for days, but after news of the catastrophic implosion that killed the pilot and his four passengers near the Titanic shipwreck, investigators are focusing on how it happened — and if it could have been prevented.

Deep-sea robots will continue searching the North Atlantic sea floor for clues. Investigators in Canada are looking at the Titan's Canadian-flagged support ship. U.S. authorities are looking into other aspects of the tragedy.

The Titan, owned by undersea exploration company OceanGate Expeditions, had been chronicling the Titanic's decay and the underwater ecosystem around the sunken ocean liner in yearly voyages since 2021.

Authorities and experts are seeking answers: Exactly when and why did the implosion occur? Will the victims' bodies ever be found? What lessons are there for the future of undersea exploration?

Here's what we know so far:

WHEN AND WHERE DID THE TITAN GO MISSING?

The craft submerged Sunday morning, and its support vessel lost contact with it about an hour and 45 minutes later, according to the Coast Guard.

The vessel was reported overdue about 435 miles (700 kilometers) south of St. John’s, Newfoundland, according to Canada’s Joint Rescue Coordination Centre in Halifax, Nova Scotia.

The Titan was launched from an icebreaker that was hired by OceanGate and formerly operated by the Canadian Coast Guard. The ship has ferried dozens of people and the submersible craft to the North Atlantic wreck site, where the Titan has made multiple dives.

WHAT HAPPENED ABOARD THE TITAN?

The vessel suffered a catastrophic implosion, killing all five aboard, sometime after it submerged Sunday morning. It's not clear exactly when or where the implosion occurred, but a U.S. Navy acoustics system detected an “anomaly” Sunday that was likely the Titan’s fatal implosion.

The Coast Guard announced that debris from the submersible had been found and the end of rescue efforts Thursday, bringing a tragic close to a saga that included an urgent around-the-clock search and a worldwide vigil for the missing vessel.

A deep-sea robot discovered the debris, near the Titanic shipwreck, that authorities say came from the submersible.

WHAT HAPPENED TO THE OCCUPANTS WHEN THE TITAN IMPLODED?

Experts say the catastrophic implosion likely killed its pilot and four passengers instantly amid the intense water pressure in the deep North Atlantic.

Maritime researchers called an implosion the worst possible outcome of all the scenarios envisioned during the desperate round-the-clock search to find the missing vessel.

Experts had cautioned that under intense pressure at extreme depths the Titan’s hull could implode, which would result in instant death for anyone aboard.

While OceanGate Expeditions, which owned and operated the craft, touted the Titan’s roomier cylinder-shaped cabin made of a carbon-fiber, industry experts say it was a departure from the sphere-shaped cabins — considered ideal because water pressure is exerted equally on all areas — made of titanium used by most submersibles.

The 22-foot long (6.7-meter long), 23,000-pound (10,432-kilogram) Titan’s larger internal volume — while still cramped with a maximum of five seated people — meant it was subjected to more external pressure.

The water pressure at 12,500 feet (3,800 meters) below the surface at the site of the Titanic wreck is roughly 400 atmospheres or 6,000 pounds per square inch.

WHO WAS KILLED?

The Titan victims are: Oceangate chief executive and Titan pilot Stockton 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.

Worldwide condolences have poured in, offering tributes to the men and support for their families.

“These men were true explorers who shared a distinct spirit of adventure, and a deep passion for exploring and protecting the world’s oceans,” OceanGate said in a statement. “We grieve the loss of life and joy they brought to everyone they knew.”

WHO REGULATES DEEP-SEA EXPEDITIONS?

The Titan’s voyage down into the North Atlantic highlights the murkily regulated waters of deep-sea exploration. It’s a space on the high seas where laws and conventions can be sidestepped by risk-taking entrepreneurs and the wealthy tourists who help fund their dreams. At least for now.

The Titan operated in international waters, far from the reach of many laws of the United States or other nations. It wasn’t registered as a U.S. vessel or with international agencies that regulate safety, nor was it classified by a maritime industry group that sets standards on matters such as hull construction.

Stockton Rush, the OceanGate Expeditions CEO and Titan pilot who was among the dead, had said he didn’t want to be bogged down by such standards.

WHAT'S NEXT?

The Coast Guard will continue searching near the Titanic for more clues about what happened to the Titan.

Officials say there is not a timeframe for when they will call off the effort, and the prospect of finding or recovering remains is unknown.

The Transportation Safety Board of Canada said Friday it’s launching an investigation involving the loss of the Titan that will focus on the cargo vessel Polar Prince.

Polar Prince is a Canadian-flagged ship that served as mothership to the Titan submersible. The Transportation Safety Board will investigate the Polar Prince in its role as a support vessel and will conduct a safety investigation into the circumstances of the operation, the agency said.

Experts say wrongful death and negligence lawsuits are also likely next in the Titan case — and they could be successful. But legal actions will face various challenges, including waivers likely signed by the Titan passengers that warned of the myriad ways they could die.

HOW MUCH DID THE SEARCH COST?

The cost of the search will easily stretch into the millions of dollars for the U.S. Coast Guard alone. The Canadian Coast Guard, U.S. Navy and other agencies and private entities also rushed to provide resources and expertise.

There’s no other comparable ocean search, especially with so many countries and even commercial enterprises being involved, said Norman Polmar, a naval historian, analyst and author based in Virginia.

The aircraft, alone, are expensive to operate.

The Pentagon has put the hourly cost at tens of thousands of dollars for turboprop P-3 Orion and jet-powered P-8 Poseidon sub hunters, along with C-130 Hercules, all utilized in the search.

Some agencies can seek reimbursements. But the U.S. Coast Guard is generally prohibited by federal law from collecting reimbursement pertaining to any search or rescue service, said Stephen Koerting, a U.S. attorney in Maine who specializes in maritime law.

News from © The Associated Press, 2023