As the investigation continues into how and when the Titan submersible imploded while on a deep-sea voyage to the Titanic wreckage last weekend, a submersible expert says he warned the vessel's CEO about safety concerns after a trip years ago.

When Karl Stanley was aboard the Titan for an underseas excursion off the coast of the Bahamas in April 2019, he felt there was something wrong with the vessel when loud noises were heard.

The day after his trip, Stanley sent an email to Stockton Rush, the CEO of the vessel's operator OceanGate Expeditions, sounding the alarm on suspected defects.

"What we heard, in my opinion ... sounded like a flaw/defect in one area being acted on by the tremendous pressures and being crushed/damaged," Stanley wrote in the email, a copy of which has been obtained by CNN.

"From the intensity of the sounds, the fact that they never totally stopped at depth, and the fact that there were sounds at about 300 feet that indicated a relaxing of stored energy /would indicate that there is an area of the hull that is breaking down/ getting spongy," Stanley continued.

The Titan imploded Sunday while on its way to the iconic Titanic wreck, killing all five passengers on board, authorities said. Those killed were Rush; British businessman Hamish Harding; French diver Paul-Henri Nargeolet; and Pakistani-born businessman Shahzada Dawood and his son, Suleman, who were British citizens.

The implosion is currently under investigation by the Transportation Safety Board of Canada and US Coast Guard. Military experts found debris consistent with the loss of the small vessel's pressure chamber, US Coast Guard Rear Adm. John Mauger said.

In his 2019 email, Stanley also asked Rush whether he would consider taking people to see the Titanic without knowing the origins of the clatters. OceanGate offered rides on Titan to passengers wanting the opportunity to view the famous wreckage.

"A useful thought exercise here would be to imagine the removal of the variables of the investors, the eager mission scientists, your team hungry for success, the press releases already announcing this summer's dive schedule," Stanley wrote.

"Imagine this project was self-funded and on your own schedule. Would you consider taking dozens of other people to the Titanic before you truly knew the source of those sounds ??" Stanley asked Rush in the email.

When asked for comment about Stanley's email, a spokesman for OceanGate told CNN they were unable to provide any additional information at this time.

Stanley told CNN's Anderson Cooper on Friday that although Rush did not respond to him in writing, Rush likely rebuilt the vessel using the same material Boeing uses to build their planes.

"He canceled that year's dives and took that carbon fiber and cut it up, found the defects and made a new one at the cost, I believe, of well over $1 million," Stanley said.

Boeing said in a statement Wednesday it was not a partner in the construction of the Titan, despite a 2021 news release from OceanGate listing the aerospace company as a "partner" that provided "design and engineering support."

OceanGate told CNN it couldn't provide more information about its relationship with Boeing. CNN has reached out to OceanGate for further comment on the company's dives in 2019.

Asked whether he was confident in the submersible's capability to make the journey to the historic shipwreck, Stanley said he believed Rush took steps to correct the problem after the email.

"He never got into the nitty-gritty with me about exactly how many model tests he had done, exactly where they failed. But my impression was that he had done enough diligence that lives were not at risk," Stanley said.

Officials working to establish what happened

With the investigation underway, officials are trying to figure out exactly how and when the implosion occurred.

To that end, remotely operated vehicles will remain on the scene and continue to gather information from the sea floor, Mauger, the US Coast Guard Rear Adm, said Thursday.

The vehicles are working to map out the vessel's debris field, which is more than 2 miles deep in the North Atlantic, Mauger said.

A second mission of the Odysseus 6K ROV began late Friday morning to continue searching and mapping efforts, said Jeff Mahoney, spokesperson for Pelagic Research Services, a company that specializes in ocean expedition.

Any attempts to recover anything from the debris field will warrant a larger operation in tandem with Deep Energy, another company helping with the mission, because the debris will likely be too heavy for Pelagic's ROV to lift by itself, Mahoney told CNN. The recovery efforts would include using rigged cabling to pull up any debris.

ROV missions are expected to continue for about another week, according to Mahoney.

Meanwhile, determining a specific timeline of events will take time because the case is "incredibly complex," Mauger explained. The Coast Guard will eventually have more information about what went wrong and its assessment of the emergency response, he noted.

"This is an incredibly difficult and dangerous environment to work in out there," Mauger said.

OceanGate co-founder Guillermo Sohnlein urged people not to rush judgment over the implosion.

"There are teams on site that are still going to be collecting data for the next few days, weeks, maybe months, and it's going to be a long time before we know exactly what happened down there," Sohnlein told CNN on Friday. "So I would encourage us to hold off on speculation until we have more data to go on."

'That could've been us'

After the tragic loss of the vessel, a father and his son who contemplated riding the Titan shared that they decided not to take the trip due to safety concerns.

Jay Bloom and his son Sean told CNN's Erin Burnett on Friday they were worried about the submersible's ability to travel that deeply into the ocean -- the Titanic wreckage is around 12,500 feet below sea level.

"I saw a lot of red flags," Sean said after he was shown a video of Rush walking through the submersible and its features.

Jay shared a text message exchange between him and Rush, who offered them the spots on the vessel for a May expedition.

Rush flew out to Las Vegas in March to try and get Jay to buy the tickets, they said. Jay noted that Rush flew in on a two-seater experimental plane he built.

"He has a different risk appetite than I do," Jay said.

Both Jay and Sean said Rush brushed off questions and concerns they had about the submersible.

"He had so much passion for the project that he was blinded by it," Jay said. "He didn't look at the things that I saw and that others saw that were problematic because it didn't fit his narrative."

The Blooms said they will not consider an experience like this ever again after they watched the news of what happened.

"All I could see when I saw that father and son was myself and my son. That could've been us," Jay said.