U.S. Coast Guard officials conceded they are facing a daunting investigation to determine what caused the Titan submersible to implode underwater near the wreckage of the Titanic, killing all five explorers aboard.

Officials said the 21-foot-long Titan was found in pieces by a remotely operated vehicle on a smooth section of ocean floor more than 2 miles beneath the surface.

"This was an incredibly complex case and we're still working to develop details for the timeline involved with this casualty and the response," Mauger said.

Read more about the investigation here.

-ABC News' Bill Hutchinson

The Titan submersible suffered a "catastrophic implosion," the U.S. Coast Guard determined.

At the depth of the Titanic, which sits 3,800 meters below sea level, the pressure reaches a level 380 times the atmospheric pressure on the Earth's surface, Stefan Williams, a professor of marine robotics at the University of Sydney, said in a blog post on Tuesday.

A fault or failure in the hull of the Titan could have led to an implosion, as the vessel gave way to the high pressure of the deep sea, Williams said.

The implosion of a submersible delivers immense force, oceanographer Bob Ballard told ABC News on Thursday.

Read more here.

-ABC News' Max Zahn

A senior U.S. Navy official confirmed to ABC News that an underwater acoustic detection system heard on Sunday what was likely the implosion of the Titan submersible. The information was immediately shared with the U.S. Coast Guard on Sunday and analysis continued afterwards.

"The U.S. Navy conducted an analysis of acoustic data and detected an anomaly consistent with an implosion or explosion in the general vicinity of where the Titan submersible was operating when communications were lost," the senior official told ABC News in a statement. "While not definitive, this information was immediately shared with the Incident Commander to assist with the ongoing search and rescue mission."

According to the official, "This information was considered with the compilation of additional acoustic data provided by other partners and the decision was made to continue our mission as a search and rescue and make every effort to save the lives on board.”

Separately, a U.S. defense official said an analysis of the “banging” noises picked up by sonar buoys were not from the missing submersible but were either natural ocean sounds, biological noises or noises associated with the surface response vessels.

-ABC News' Luis Martinez

Hamish Harding, a British businessman who was among the five people killed in the Titan implosion, was remembered as a "passionate explorer" by his loved ones.

"Hamish Harding was a loving husband to his wife and a dedicated father to his two sons, whom he loved deeply," a statement sent on behalf of his family and Action Aviation, the company he chaired, said. "To his team in Action Aviation, he was a guide, an inspiration, a support, and a Living Legend."

"He was one of a kind and we adored him. He was a passionate explorer -- whatever the terrain -- who lived his life for his family, his business and for the next adventure," the statement continued. "What he achieved in his lifetime was truly remarkable and if we can take any small consolation from this tragedy, it's that we lost him doing what he loved."

-ABC News' Mark Guarino