An international group of agencies is investigating what may have caused the Titan submersible to implode while carrying five people to the Titanic wreckage, and US maritime officials say they’ll issue a report aimed at improving the safety of submersibles worldwide.

Investigators from the US, Canada, France and the United Kingdom are working closely together on the probe of the June 18 accident, which happened in an “unforgiving and difficult-to-access region” of the North Atlantic, said US Coast Guard Rear Adm. John Mauger, of the Coast Guard First District.

Salvage operations from the sea floor are ongoing, and the accident site has been mapped, Coast Guard chief investigator Captain Jason Neubauer said Sunday. He did not give a timeline for the investigation. Neubauer said the final report will be issued to the International Maritime Organization.

“My primary goal is to prevent a similar occurrence by making the necessary recommendations to advance the safety of the maritime domain worldwide,” Neubauer said.

Evidence is being collected in the port of St John’s, Newfoundland, in coordination with Canadian authorities.

All five people on board the Titan were killed. Debris from the vessel was located about 12,500 feet (3,810 metres) underwater and roughly 1,600 feet (488 meters) from the Titanic on the ocean floor, the Coast Guard said last week.

One of the experts whom the Coast Guard has been consulting said Monday that he doesn’t believe there is any more evidence to collect.

“It is my professional opinion that all the debris is located in a very small area and that all debris has been found,” said Carl Hartsfield, a retired Navy captain and submarine officer who now directs a lab at the Woods Hole Oceanographic Institution that designs and operates autonomous underwater vehicles.

Early summer is the best time to be conducting this type of operation because of the lower likelihood of storms, but it’s still likely to be painstaking, said Donald Murphy, an oceanographer who served as chief scientist of the Coast Guard’s International Ice Patrol.

The search is taking place in a complex ocean environment where the Gulf Stream meets the Labrador Current, an area where challenging and hard-to-predict ocean currents can make controlling an underwater vehicle more difficult, Murphy said.

But Hartsfield said based on the data he’s reviewed and the performance of the remote vehicles so far, he doesn’t expect currents to be a problem. Also working in the searchers’ favour, he said, is that the debris is located in a compact area and the ocean bottom where they are searching is smooth and not near any of the Titanic debris.

Authorities are still trying to sort out what agency or agencies are responsible for determining the cause of the tragedy, which happened in international waters.

OceanGate Expeditions, the company that owned and operated the Titan, is based in the US but the submersible was registered in the Bahamas. Meanwhile, the Titan’s mother ship, the Polar Prince, was from Canada, and those killed were from England, Pakistan, France, and the US.