Repeated red flags raised by experts about the Titan's safety are likely to feature in investigations into the tragedy

• Submersible experts raised red flags about the Titan's safety long before it imploded.
• Those warnings will play an important part in investigations into the implosion, officials said.

Investigations into the implosion of OceanGate's Titan submersible are likely to examine repeated warnings about the craft's safety and design.

Investigators searched the Canadian research ship the Polar Prince, which took the Titan into international waters, on Saturday after it returned to port in Newfoundland, per The New York Times.

Staff from the Transportation Safety Board of Canada and the Royal Canadian Mounted Police searched the ship as what looks to be a lengthy investigation into the fatal voyage begins.

Relatives of the five people who died on the Titan, its past passengers, and crew of the Polar Prince, were being interviewed, per the Times.

But it's also expected that investigators will examine past warnings by experts, engineers, and former employees about the seaworthiness of the submersible.

Speaking on Thursday, US Coast Guard Rear Adm. John Mauger said safety and regulations were likely to be the "focus for future review."

Submersible experts raised red flags about the Titan's safety long before it imploded but OceanGate continued its expeditions.

The company was even sued in 2018 by a former employee after he highlighted concerns he had with the sub, which was not independently certified, and said it needed more testing.

OceanGate's former director of marine operations, David Lochridge, also warned the company about inadequate "quality control and safety" protocols. He said Stockton Rush, the CEO who also died on the Titan, had asked him to carry out a quality inspection of the sub.

Lochridge claimed in the suit that he addressed his uneasiness with the sub's safety with management, but was fired and accused of breach of contract. The case was settled out of court in November 2018.

In a since-deleted blog post titled "Why Isn't Titan Classed?", which is archived online, the company wrote that getting the Titan classed would be a lengthy process, and that could stifle innovation.

"Bringing an outside entity up to speed on every innovation before it is put into real-world testing is anathema to rapid innovation," OceanGate stated.

A former OceanGate consultant also reportedly warned Rush, the OceanGate cofounder, that he was putting passengers in danger.

"Until a sub is classed, tested and proven it should not be used for commercial deep dive operations," Rob McCallum told Rush, according to emails seen by BBC News. "I implore you to take every care in your testing and sea trials and to be very, very conservative."

Rush responded and said he was "tired of industry players who try to use a safety argument to stop innovation".