Renowned Hollywood director and Titanic researcher James Cameron said he believes the carbon-fiber composite construction of the submersible's hull was the "critical failure" that led to its implosion during a deep-sea tour of the Titanic wreckage.

"You don't use composites for vessels that are seeing external pressure. They're great for internal pressure vessels like scuba tanks, for example, but they're terrible for external pressure," Cameron, who famously directed the Oscar-winning film "Titanic," told ABC News' George Stephanopoulos in an interview Friday on "Good Morning America."

"This was trying to apply aviation thinking to a deep-submergence engineering problem. We all said that it was, you know, a flawed idea and they didn't go through certification," he continued. "I think that was a critical failure.

"The thing that's insidious here," Cameron added, is the way these materials "fail at pressure."

"They fail over time, each dive adds more and more microscopic damage," he said. "So, yes, they operated the sub safely at Titanic last year and the year before, but it was only a matter of time before it caught up with them."

OceanGate CEO Stockton Rush, who was among the five crew members killed on the submersible, had previously defended the decision to manufacture the Titan with the material, saying he believed a sub made with carbon fiber would have a better strength-to-buoyancy ratio than titanium.

Bob Ballard, the oceanographer and explorer who discovered the Titanic wreckage in 1985, told ABC News that he expects the investigation into what happened "will go on for quite some time."

"There will be now a very systematic survey. I've done this before," he said during the interview Friday morning. "The [remotely operated vehicles] are going to do a very, very precise, systematic mapping that will collect the photography and high-definition imagery and they'll also be recovering the objects."

The Hussain and Kulsum Dawood family has issued a statement expressing their condolences.

"It is with profound grief that we announced the passing of Shahzada and Suleman Dawood," the family said. "Our beloved sons were aboard OceanGate's Titan submersible that perished underwater. Please continue to keep the departed souls and our family in your prayers during this difficult period of mourning."

"We are truly grateful to all those involved in the rescue operations," they continued. "Their untiring efforts were a source of strength for us during this time. We are also indebted to our friends, family, colleagues and well-wishers from all over the world who have stood by us during our hour of need. The immense love and support we receive continues to help us endure this unimaginable loss."

"We extend our heartfelt condolences to the families of the other passengers on the Titan submersible," the family added. "At this time, we are unable to receive calls and request that support, condolences and prayers be messaged instead. Details of their final rites in this world will be announced soon."

-ABC News' Habibullah Khan

Engro, the company sub passenger Shahzada Dawood worked as the vice chairman, offered its condolences for both Dawood and his son, Suleman Dawood, on Thursday.

"With heavy hearts and great sadness, we grieve the loss of our vice chairman, Shahzada Dawood, and his beloved son, Suleman Dawood," the company said in the message. "Our thoughts and prayers are with the Dawood family at this tragic time."

"We extend our heartfelt condolences to the family, colleagues, friends and all those around the world who grieve this unthinkable loss," it added.

-ABC News' Habibullah Khan

The submersible that catastrophically imploded while on a voyage to see the Titanic wreckage has highlighted a high-risk, experimental and exclusive tourism opportunity to see what is largely considered to be the most famous shipwreck of all time.

The doomed ocean liner has intrigued the public from the moment it tragically crashed into an iceberg in the Atlantic Ocean and sank on April 15, 1912 -- as well as throughout the century-plus since.

Visits to the underwater site have been conducted in recent decades to retrieve artifacts, study the Titanic's gradual decay and simply lay eyes on the storied shipwreck, which has inspired a wealth of novels, plays, TV shows and films.

"The Titanic has basically been in popular culture since the night it sank," Robert Thompson, founding director of the Bleier Center for Television and Popular Culture at Syracuse University, told ABC News.

Read more about the Titanic's long intrigue here.

The U.S. Coast Guard announced via Twitter early Thursday that a remotely operated vehicle (ROV) deployed by the Canadian vessel Horizon Arctic has reached the sea floor, beginning its search for the missing submersible.

Meanwhile, the French vessel L'Atalante is preparing its ROV to enter the water in the search area, the U.S. Coast Guard said.