Footballer Emiliano Sala and his pilot were exposed to harmful levels of carbon monoxide inside the cockpit of their private plane before it crashed in to the Channel in January, air accident investigators said.
The plane went down on 21 January off the coast of Guernsey, killing him and his pilot, David Ibbotson.
Toxicology tests of Sala showed a carboxyhaemoglobin (a mixture of carbon monoxide and haemoglobin) saturation level of 58%.
According to investigators, this is enough to cause seizures, unconsciousness and a heart attack.
Investigators also assume that the pilot would also have been affected by exposure to the gas.
The team of investigators are now working with the aircraft manufacturers, and the US National Transportation Safety Board, to identify possible ways that carbon monoxide might have entered the aircarft’s cabin.
The wreckage of the plane was located on the 3 February this year, and was later recovered.
A body in the wreckage was identified as that of the Argentinian footballer.