The family of a French explorer who died in a submersible implosion has filed a more than $50 million lawsuit, saying the crew experienced “terror and mental anguish” before the disaster and accusing the sub’s operator of gross negligence.

Paul-Henri Nargeolet was among five people who died when the Titan submersible imploded during a voyage to the famed Titanic wreck site in the North Atlantic in June 2023. No one survived the trip aboard the experimental submersible owned by OceanGate, a company in Washington state that has since suspended operations.

Known as “Mr. Titanic,” Nargeolet participated in 37 dives to the Titanic site, the most of any diver in the world, according to the lawsuit. He was regarded as one of the world’s most knowledgeable people about the famous wreck. Attorneys for his estate said in an emailed statement that the “doomed submersible” had a “troubled history,” and that OceanGate failed to disclose key facts about the vessel and its durability.

According to the lawsuit, the Titan “dropped weights” about 90 minutes into its dive, indicating the team had aborted or attempted to abort the dive.

“While the exact cause of failure may never be determined, experts agree that the Titan’s crew would have realized exactly what was happening,” the lawsuit states. “Common sense dictates that the crew were well aware they were going to die, before dying.”

The lawsuit goes on to say: “The crew may well have heard the carbon fiber’s crackling noise grow more intense as the weight of the water pressed on Titan’s hull. The crew lost communications and perhaps power as well. By experts’ reckoning, they would have continued to descend, in full knowledge of the vessel’s irreversible failures, experiencing terror and mental anguish prior to the Titan ultimately imploding.”