Four people who died when the Bayesian superyacht sank off the coast of Sicily last month suffocated after oxygen depleted in a pocket of air they were trapped in, the Italian news agency Ansa has reported.
Banking executive Jonathan Bloomer, his wife Judy Bloomer, lawyer Chris Morvillo and his wife Neda Morvillo were among the seven people who lost their lives when the vessel went down during a violent storm.
Post-mortem examinations revealed that none of them had water in their lungs, suggesting they did not drown, according to reports.
British tech entrepreneur Mike Lynch, his 18-year-old daughter Hannah Lynch and the yacht's chef, Recaldo Thomas, also died in the incident.
The group was travelling on the yacht following Mr Lynch's acquittal of fraud charges in the United States earlier this year.
Investigators believe the cabin the four were found in filled with carbon dioxide as the oxygen supply diminished, leading to their deaths.
According to Italian media, divers involved in recovering the bodies found the victims on the left side of the cabins, an indication that they had been trying to reach the last remaining air pockets as the vessel tilted to the right during the sinking.
There were also no signs of external injuries on the four victims.
The remaining post-mortems for Mr Lynch, his daughter Hannah, and Mr Thomas are expected to take place over the next few days.
Mr Lynch’s wife, Angela Bacares, survived the incident along with 14 others on board.
The superyacht will be raised from the seabed as the investigation continues.
Italian prosecutors have opened an inquiry into suspected manslaughter, placing the boat’s captain, James Cutfield, and two British crew members, Tim Parker Eaton and Matthew Griffiths, under investigation.
Being investigated does not equate to being charged and is a procedural step.
Allegations of whether negligence may have contributed to the yacht's sinking, such as leaving external doors open, will form part of the investigation.