A structural problem with the Titan sub’s hull could have led to the “catastrophic implosion” that destroyed the vessel and killed all five people aboard, experts say.

OceanGate-owned submersible fell apart as it descended toward the Titanic wreckage this week, and investigators were looking for clues on Friday.

The cause of the deep-sea disaster is still unclear, but one expert believes the sub’s hull – its main body – may have failed.

According to Virginia Tech ocean engineering professor Stefano Brizzolara, the sub’s pressure hull may have fractured under pressure and caused the implosion.

“It is difficult to say what caused the structural failure in this case, but any small material and geometric imperfection, misalignment of connection flanges, tightening torque of bolted connection may have started the structural collapse,” Brizzolara said.

There were two different materials used to construct the Titan’s hull: carbon fiber-reinforced plastic and titanium.

When it fails, the carbon fiber element can break into small fragments, as it is “very prone to possible defects” and “has a more fragile behavior” than other materials.

Titan’s repeated voyages to the wreckage of the ocean liner may have also caused the hull to deform and shrink.

“These repeated deformation cycles may have started some material defects in the [carbon reinforced plastic] or some permanent deformations or misalignment between the two parts of the hull that were built with two different materials, which deform in a different way,” he said.

When the implosion occurred, any small leak at that depth would have sent water rushing in at a speed of about 1,000 km (621 miles) per hour, Brizzolara said.