Footballer Emiliano Sala was exposed to high levels of carbon monoxide prior to a fatal plane crash in the English Channel, a report has revealed.
Sala, 28, and pilot David Ibbotson crashed on January 21 while traveling to Cardiff from Nantes in France.
Toxicology tests on Sala's body showed CO levels in his blood were so great it could have caused a seizure, unconsciousness or a heart attack.
The Sala family's lawyer said the report raised further questions.
Mr Ibbotson, from Crowle, North Lincolnshire, has still not been found, but it is likely he would also have been exposed to carbon monoxide, the Air Accidents Investigation Branch (AAIB) report said.
Sala's blood had a COHb (carboxyhaemoglobin - which forms in red blood cells upon contact with carbon monoxide) level of 58%.
At this level, symptoms would include seizure, unconsciousness and heart attack, the report said.
Piston engine aircraft such as the Piper Malibu involved in the crash produce high levels of carbon monoxide, the report said.
The gas is normally conveyed away from the aircraft through the exhaust system, but poor sealing or leaks into the heating and ventilation system can enable it to enter the cabin.
Several devices are available to alert pilots over the presence of carbon monoxide.
The AAIB said they are not mandatory but can "alert pilots or passengers to a potentially deadly threat".