Investigators from Canada have boarded the main support ship of the Titan submersible after it returned to port in Newfoundland on Saturday.
Flags on board the Polar Prince were at half-mast as it arrived at the port in St John’s. Police and safety investigators could be seen boarding shortly after it docked.
The Transportation Safety Board (TSB) of Canada announced that the Polar Prince would be the subject of an investigation after five men were killed in what is understood to be a “catastrophic implosion” of the Titan submersible near the Titanic wreck site.
The TSB said the US Coast Guard will lead the investigation after they declared the loss of Titan to be a “major marine casualty”.
Rib boats could be seen towing what appeared to be the Titan submersible’s launch platform away from the Polar Prince and further along the port.
Canadian Coast Guard (CCG) boats had already started to return to St John’s harbour on Friday as the recovery operation began to wind down.
In a statement issued before ships began to return to the port, the CCG said the search and rescue operation had concluded.
The CCG said one of its vessels would remain on the scene and would “provide assistance and support to the recovery and salvage operations as requested by Maritime Rescue Coordination Centre Boston”.
The TSB said a team of investigators had been deployed to St John’s to “gather information, conduct interviews and assess the occurrence”.
In its own statement, the safety body said the investigation would be carried out “in accordance with the Canadian Transportation Accident Investigation and Safety Board Act and international agreements”.
The TSB will not determine civil or criminal liability and conducts investigations for “the advancement of transportation safety”.
British-Pakistani businessman Shahzada Dawood, 48, his son Suleman, 19, and billionaire explorer Hamish Harding, 58, lost their lives on the vessel as it dived on the wreck of the Titanic on Sunday.
OceanGate CEO Stockton Rush, 61, and French Navy veteran Paul-Henri Nargeolet, 77, also died following the “catastrophic” implosion.
The five vanished on a £195,000 trip to the world’s most famous shipwreck, which lies 460 miles off Newfoundland in Canada.
Search vessels on Thursday spotted broken-off pieces of their Titan submersible including the tailcone - leading experts to conclude that the vessel must have imploded.
The search for the vessel sparked a huge international search effort with rescue teams from the US, Canada and France.
It comes after it was revealed that the US Navy detected sounds “consistent with an detecte consist implosion” shortly after Titan lost contact on Sunday.
A navy official told US media outlets their information about the “acoustic anomaly” had been used by the US Coast Guard to narrow the search area.
It has also been revealed safety warnings over the OceanGate submersible were repeatedly dismissed by the CEO of the company, according to email exchanges with a leading deep sea exploration specialist.
In messages seen by the BBC, Rob McCallum told OceanGate boss Mr Rush that he was potentially putting his clients at risk and urged him to stop using the sub until it was classified by an independent body.
Mr Rush responded that he was "tired of industry players who try to use a safety argument to stop innovation". Mr McCallum said the exchange ended after OceanGate’s lawyers threatened legal action.
