Investigators say Emiliano Sala and his pilot David Ibbotson may have been exposed to potentially fatal levels of carbon monoxide when their aircraft crashed.
The Argentinian footballer was flying to Wales from France to join Premier League club Cardiff when his plane came down in the English Channel in January.
A report released on Wednesday by Britain's Air Accidents Investigation Branch (AAIB) said that carbon monoxide poisoning was a particular risk in the aircraft they were travelling in.
"Toxicology tests found that the passenger had a high saturation level of COHb (the combination product of carbon monoxide and haemoglobin)," AAIB revealed.
"In this type of aircraft, the cockpit is not separated from the cabin and it is considered likely that the pilot would also have been affected to some extent by exposure to CO.
"A COHb level of 50 percent or above in an otherwise healthy individual is generally considered to be potentially fatal."
Exposure to the gas can lead to damage to the brain and nervous system, with unconsciousness and heart attacks possible with COHb levels of over 50 percent.
The report “raises many questions”: Sala's family
According to Daniel Machover, a lawyer for Sala's family, "The family and the public need to know how the carbon monoxide was able to enter the cabin
"Emiliano's family call on the AAIB to salvage the wreckage of the plane without further delay."
Meanwhile, Cardiff City said it was concerned at the report's findings, and believe they show that the aircraft used was not appropriate.
A spokesperson for the club said, "We continue to believe that those who were instrumental in arranging its usage are held to account for this tragedy."
