Footballer Emiliano Sala and his pilot were exposed to harmful levels of carbon monoxide inside the cockpit of their private plane before it crashed into the Channel in January, air accident investigators have said.
The plane went down on 21 January off the coast of Guernsey, killing Sala and pilot David Ibbotson.
Toxicology tests performed on Sala showed a carboxyhaemoglobin (a mixture of carbon monoxide and haemoglobin) saturation level of 58%.
Emiliano Sala
Image:Sala had just signed for Cardiff City
According to investigators, anything over 50% is considered to be "potentially fatal" and could trigger a heart attack, seizure or unconsciousness.
They assumed that the pilot, whose body has not been found, 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 aircraft's cabin.
The Air Accidents Investigation Branch (AAIB) added: "Work is also continuing to investigate pertinent operational, technical, organisational and human factors which might have contributed to the accident."