The U.S. Coast Guard on Thu. confirmed the deaths of the passengers aboard the Titan, concluding a four-day search.

USCG Rear Adm. John Mauger told reporters Thu. that they found debris from the Titanic-bound sub on the sea floor. (CNN)

Mauger: "The debris field is consistent with a catastrophic implosion of the vessel." (CNN)

Five passengers were aboard the Titan; the sub went missing Sun. shortly after it began its descent to the Titanic. (CNN)

"Titanic" director James Cameron on Thu. lamented the loss of his friend during an interview with ABC News.

Cameron told ABC News Thu. that his friend, French explorer Paul-Henri Nargeolet, was aboard the Titan when it imploded.

Cameron: "I’ve known [him] for 25 years, and for him to have died tragically...is almost impossible for me to process."

Cameron also told ABC News that OceanGate, the company behind the Titan, was infamous in the deep-sea explorer community:

Cameron: "A number of the top players in the deep submergence...community even wrote letters to the company..."

Cameron: "...what they were doing was too experimental to carry passengers and that it needed to be certified."

Cameron is an experienced deep-sea explorer: in 2012, he piloted a sub to the deepest point in the Pacific Ocean. (NYT)

Cameron also compared the Titan's implosion to the 1912 sinking of the Titanic: "It’s a very similar tragedy..."

Cameron: "...the captain was repeatedly warned about ice ahead of his ship, and yet he steamed at full speed..."