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, 59, crashed on 21 January while travelling from Nantes in France to Cardiff.
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 said there should be a detailed examination of the plane.
Mr Ibbotson, from Crowle, North Lincolnshire, has still not been found.
What does the report say?
The Air Accidents Investigation Branch (AAIB) 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 include seizure, unconsciousness and heart attack.
It added: "A COHb level of more than 50% in an otherwise healthy person is generally considered to be potentially fatal."
It is likely Mr Ibbotson would also have been exposed to carbon monoxide.
Piston engine aircraft such as the Piper Malibu involved in the crash produce high levels of carbon monoxide.
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 – they are not mandatory but can "alert pilots or passengers to a potentially deadly threat".
What will happen next?
AAIB investigators are working with aircraft manufacturers in the USA – where the Piper Malibu was registered – to look at how carbon monoxide could have entered the cabin.
"Operational, technical and human factors" will be considered.
Geraint Herbert, the AAIB's lead inspector for this investigation, said: "Symptoms at low exposure levels [to carbon monoxide] can be drowsiness and dizziness, but as the exposure level increases, it can lead to unconsciousness and death.
"The investigation continues to look into a wide range of areas in relation to this accident, but in particular we are looking at the potential ways in which carbon monoxide can enter the cabin in this type of aircraft."
Wednesday's bulletin was the second to be released following the crash, but the investigation is not expected to report its full findings until early 2020.
How has Sala's family reacted?
Daniel Machover of Hickman & Rose solicitors, who represents the family, said: "The family believe that a detailed technical examination of the plane is necessary.
"The family and the public need to know how the carbon monoxide was able to enter the cabin. Future air safety rests on knowing as much as possible on this issue."
Why hasn't the plane been recovered?
The AAIB responded to calls for the plane to be retrieved from the sea bed by saying it filmed substantial video evidence at the scene after the aircraft was found in February.
"It was not possible at the time to recover the wreckage," it said.
"We have carefully considered the feasibility and merits of returning to attempt to recover the wreckage. In this case, we consider that it will not add significantly to the investigation and we will identify the correct safety issues through other means."
The statement said after a "violent impact with the sea", the wreckage may not even give definitive answers and the reasons for not retrieving the plane had been explained in detail to both the Sala and Ibbotson families.
What has Cardiff City said?
The club said it was "concerned" by the report, adding: "We continue to believe that those who were instrumental in arranging its [the plane's] usage are held to account for this tragedy."
In an interview in February, football agent Willie McKay, who commissioned the flight, told the BBC he and his family paid for it.
He was not involved, he said, in selecting the plane or the pilot and it was not a cost-share arrangement.
How have experts interpreted the report?
Retired pilot and aviation safety commentator Terry Tozer said the finding was "a surprise", adding: "It shows you can never tell what the root cause of an accident is until the investigators have dug into the nitty gritty.
"How and why did the carbon monoxide get in? Presumably through the exhaust system… the fumes get into the ventilation system."
Mr Tozer said he had never encountered anything similar before and would not expect carbon monoxide poisoning to be a big risk on such an aircraft.
He added: "It's not like a car where you can open the windows. It can creep up on you, and that could be a slow process.
"It's odourless so you wouldn't necessarily know you were being fed these fumes unless you had a detection system – but that isn't mandatory for this type of aircraft."
Mr Tozer agreed with the Sala family that salvaging the wreckage and examining it would be the only way to find how the leak occurred.
"Aviation accidents usually come about when a number of factors accumulate.
"So, we start with the pilot and his lack of qualifications, then circumstances that delay the flight to night time, possibly feeling pressure the pilot then takes off when he shouldn't and finds weather that he is struggling with and the final straw is that his ability is impaired by poisoning from a leak in the exhaust and he loses control."
How dangerous is carbon monoxide?
By James Gallagher, health and science correspondent, BBC News
Carbon monoxide is an invisible killer with no smell, colour or taste.
It is deadly because the gas starves the body of vital oxygen.
Your red blood cells contain haemoglobin – its job is to pick up oxygen from the lungs and transport it around the body.
The problem is haemoglobin prefers carbon monoxide and binds to the gas iRead More – Source