US Coast Guard investigating cause of Titanic submersible implosion

The U.S. Coast Guard is investigating the cause of the undersea implosion of a tourist submersible that killed all five people aboard while diving to the century-old wreck of the Titanic, officials said on Sunday.

The announcement comes a day after Canada's Transportation Safety Board said it was conducting its own investigation into the implosion, which has raised questions about the unregulated nature of such expeditions.