The four deceased who have been autopsied so far had no water in their lungs, writes the newspaper La Repubblica.
This indicates that they did not drown, but died when the cabin filled with carbon dioxide and the oxygen slowly ran out.
The hypothesis must, however, be confirmed through further tissue tests, but according to the newspaper, the forensic pathologist describes it as if they died trapped in a trap when the boat filled with water.
Five of the six bodies were found, according to reports, in the same room. The sixth, IT magnate Mike Lynch's 18-year-old daughter Hannah, lay in the cabin next door.
The remaining autopsies, on Lynch and his daughter as well as the boat's cook, will take place on Friday.
The boat's captain has been served suspicion of crime but has so far remained silent during questioning, reports the Italian newspaper La Stampa.
The luxury sailboat is believed to have been hit by sudden storm winds that surprised the crew and passengers. Seven people died when the Bayesian sank to the bottom of the sea off Sicily on August 19.
15 people were able to be rescued, including Mike Lynch's wife.
