The mysteries onboard the coal carrier Sage Sagittarius are getting deeper, with reports that a key audio recorder has gone missing.

Investigations into the notorious ‘death ship’ are playing out in NSW courts, after reports of numerous suspicious deaths, attacks, gun smuggling and other illegal behaviour.

It was hoped that the ship’s voyage data recorder – like the black box on a plane - would contain audio recordings from the upper deck of the ship, and may have captured information on the disappearance of ship’s cook Cesar Llanto on August 30, 2012.

The ship’s owner Hachiuma Steamship has told the inquest that the recordings were overwritten rather than saved.

Counsel assisting coroner Philip Strickland said shipping companies had a legal obligation to save black box data.

Hachiuma Steamship representative Kazuhiro Hayashi said he first boarded the ship to manage the situation in the days after the disappearance of chief engineer Hector Collado.

Hayashi told Australian police that he suspected Collado did not fall overboard by accident, and speculated that it might have been suicide or murder.

Hayashi was asked if he recalled suggesting the ship’s oiler Raul Vercede was involved in Collado’s death, something he denied saying.

Hayashi later said he did not know if the death was accidental, murder or suicide,

The current hearing sessions will wrap up this week, before resuming in September.