Crew onboard the mothership that towed the doomed Titan sub before its "catastrophic implosion" have been banned from leaving the vessel amid a probe.
MV Polar Prince was among four vessels which returned to St John's in Newfoundland today, after four passengers and the pilot of the underwater vehicle were killed in the incident near the wreckage of the Titanic.
As soon as the boat was secured at the dockside, it was boarded at 8am ET by a team of US and Canadian federal investigators who are now set to determine how the implosion took place.
A coastguard source told the Sunday Mirror: “None of the crew was allowed to disembark until all had been interviewed by investigators.
"Both US and Canadian governments are taking the death of the five men extremely seriously and want to know every detail about how they came to die.
"Canada’s Transportation Safety Board and the US National Transportation Safety Board have both sent investigators to the Polar Prince."
It is understood relatives of the deceased - Shahzada Dawood, 48, and his son Suleman Dawood, 19, Hamish Harding, 58, the sub’s American boss Stockton Rush, 61, and French Navy veteran Paul-Henri (PH) Nargeolet, 77 - were in St John’s when the ships arrived home.
Hours ahead of the Polar Prince's arrival into St John’s Harbour were the Canadian coastguard ships, Ann Harvey and Terry Fox and offshore vessel, Skandi Vinland.
All had taken part in the mammoth search and rescue operation that involved British, American and Canadian personnel.
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".
The investigation comes after the BBC reported that emails from Mr Rush showed he had dismissed safety concerns over the Titan submersible.
In the exchanges with deep-sea exploration specialist Rob McCallum, OceanGate's chief executive said he was "tired of industry players who try to use a safety argument to stop innovation".
The Titan submersible lost contact with the tour operator an hour and 45 minutes into the two-hour descent to the wreckage, with the vessel reported missing eight hours after communication was lost.
In the days that followed the gone-missing report, the US Coast Guard said the vessel had a depleting oxygen supply that was expected to run out on Thursday.
A report from The Wall Street Journal said the US navy had detected a sound in the search area for the submersible on Sunday that was consistent with an implosion.
The navy reportedly passed on the information to the Coast Guard, which continued its search because the data was not considered by the navy to be definitive.
