PORTLAND, Maine (AP) — A year after an experimental submersible imploded en route to the Titanic, unanswered questions linger — with no immediate answers.

Tuesday marks one year since the Titan vanished on its way to the historic wreckage site. After a five-day search that captured the world’s attention, officials said the craft had been destroyed and all five people on board killed.

The U.S. Coast Guard quickly convened a high-level investigation into what happened. Concerns leading up to the investigation included the Titan’s unconventional design and its creator’s decision to forgo standard independent checks.

A look at the one-year anniversary of the Titan tragedy:

The investigation is taking longer than expected

Coast Guard officials said in a statement last week that they would not be ready to release the results of their investigation by the anniversary. A public hearing to discuss the findings won’t happen for at least two more months, they said.

Investigators “are working closely with our domestic and international partners to ensure a comprehensive understanding of the incident,” Marine Board of Investigation Chair Jason Neubauer said, describing the inquiry as a “complex and ongoing effort.”

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The Titan was owned by a company called OceanGate, which suspended its operations last July, not long after the tragedy. OceanGate declined to comment.

The Titan made its last dive on June 18, 2023, a Sunday morning, and lost contact with its support vessel about two hours later. When it was reported overdue that afternoon, rescuers rushed ships, planes and other equipment to the area, about 435 miles (700 kilometers) south of St. John’s, Newfoundland. The Transportation Safety Board of Canada said Monday that there are other submersibles operating within Canadian waters, some of which are not registered with any country.

In addition to OceanGate co-founder Stockton Rush, the implosion killed two members of a prominent Pakistani family, Shahzada Dawood and his son Suleman Dawood; British adventurer Hamish Harding; and Titanic expert Paul-Henri Nargeolet.

Remembering those who died

David Concannon, a former adviser to OceanGate, said he will mark the anniversary privately with a group of people who were involved with the company or the submersible’s expeditions over the years, including scientists, volunteers and mission specialists.

Harding and Nargeolet were members of The Explorers Club, a professional society dedicated to research, exploration and resource conservation.

“Then, as now, it hit us on a personal level very deeply,” the group’s president, Richard Garriott, said in an interview last week.

Garriott said there will be a remembrance celebration for the Titan victims this week in Portugal at the annual Global Exploration Summit.

The tragedy won’t stop deep-sea exploration

The Georgia-based company that owns the salvage rights to the Titanic plans to visit the sunken ocean liner in July using remotely operated vehicles, and a real estate billionaire from Ohio has said he plans a voyage to the shipwreck in a two-person submersible in 2026.

Several deep-sea explorers told The Associated Press that the Titan disaster shook the worldwide community of explorers, but it remains committed to continuing its missions to expand scientific understanding of the ocean.

Garriott believes the world is in a new golden age of undersea exploration, thanks to technological advances that have opened frontiers and provided new tools to more thoroughly study already visited places. The Titan tragedy hasn’t tarnished that, he said.

“Progress continues,” he said. “I actually feel very comfortable and confident that we will now be able to proceed.”

Veteran deep-sea explorer Katy Croff Bell said the Titan implosion reinforced the importance of following industry standards and performing rigorous testing. But in the industry as a whole, “the safety track record for this has been very good for several decades,” said Bell, president of Ocean Discovery League, a nonprofit organization.

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Ramer reporter from Concord, New Hampshire.