The Titan submersible, which disappeared after setting off to tour the wreckage of the Titanic on Sunday, experienced a “catastrophic implosion,” US Coast Guard Rear Admiral John Mauger announced during a press conference on Thursday afternoon.

“This morning, an ROV, or remote-operated vehicle from the vessel Horizon Arctic discovered the tail cone of the Titan submersible approximately 1,600 feet from the bow of the Titanic on the seafloor,” Mauger stated. “The ROV subsequently found additional debris. In consultation with experts from within the unified command, the debris is consistent with the catastrophic loss of the pressure chamber.”

The Titan is a 22-foot long, 20,000-pound submersible owned by OceanGate Expeditions, a Titanic tourism company that takes guests on underwater journeys for $250,000 per person. On Sunday, five crew members boarded the Titan sub with the hopes of seeing the remains of the Titanic that lies around 13,000 feet in the ocean.

However, the submersible, which doesn’t have a GPS and receives directions over text messages from a support ship, lost contact with the crew on the surface shortly after its departure. As search crews from the US and Canada flooded the area in the days that followed, concerns began to grow about the submersible’s status and its dwindling oxygen supply.

The five passengers included OceanGate CEO Stockton Rush, British businessman Hamish Harding, French diver Paul-Henri Nargeolet, as well as the British-Pakistani businessman Shahzada Dawood and his 19-year-old son, Suleman. In a statement issued in response to the Coast Guard’s findings, OceanGate said it believes the sub’s passengers “have sadly been lost.”

The search crew discovered five components consistent with the Titan, including its nose cone, the front-end bell of the pressure hull, and pieces that comprised the “totality” of the pressure vessel. It’s still not clear when — or why — the implosion occurred, but the Coast Guard says it will continue investigating the incident.

“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 says. “Our hearts are with these five souls and every member of their families during this tragic time. We grieve the loss of life and joy they brought to everyone they knew.”

Several experts raised concerns about the safety of the Titan over the course of several years, with one former OceanGate employee, David Lochridge, getting fired after calling attention to the integrity of the submersible, according to a report from Reuters. Last year, CBS correspondent David Pogue commented on the sub’s “jerry-rigged” design before embarking on a tour of the Titanic with OceanGate.