An intense, four-day international hunt for a submersible containing Titanic tourists has ended, but questions remain about not only what happened but why it was allowed to.

The five-passenger submersible was billed as state of the art by operator OceanGate Expeditions. It featured newer, lighter materials and an elongated shape that made it able to ferry more undersea tourists than any other deep-dive vessel.

But the unique design hadnt been widely tested or classed by a third-party agency. The company and its CEO and co-founder Stockton Rush, who was among those killed in last weeks dive, argued the lengthy process to do so would stifle innovation, as Rush told Smithsonian Magazine in 2019.