Cook agent Susan Cooper and husband John died within hours of each other while staying at the Steigenberger Aqua Magic hotel in the Red Sea resort of Hurghada last month.
The Egyptian authorities said the couple died of natural causes, while Cook said there was no evidence carbon monoxide poisoning was a factor in their deaths.
The couple’s daughter, Kelly Ormerod, who was staying at the same hotel, has maintained in the weeks following her parents’ deaths there was an unusual smell in their room the morning they were taken seriously ill.
Now, The Times reports the room next to the Coopers’ was fumigated shortly before the couple died.
Citing a report by the Egyptian authorities, due to be published on Wednesday, The Times said a contractor fumigated the room with an insecticide, lambda-Cyhalothrin, on August 20.
The paper said the location of the Coopers’ room meant the only escape route for the fumes was into their room.
A Thomas Cook spokesperson said: “We await the results of the Egyptian authorities’ investigation into the tragic deaths of Mr and Mrs Cooper.”
The operator conducted its own tests at the hotel following the Coopers’ deaths, which found a “high level of E. coli and staphylococcus bacteria”, but have since been ruled inconclusive.
Cook chief executive Peter Fankhauser previously said 13 Cook guests staying at the Steigenberger were suffering food poisoning when the Coopers died.
Fankhauser has since apologised, stating “standards fell below” what Cook expects from its hotel partners while adding it was “clear something went wrong in August”.
Cook pulled all 300 of its guests out of the hotel following the Coopers’ deaths.
The forthcoming report by the Egyptian authorities is expected to reveal details of a post-mortem into the deaths of Susan and John Cooper.
These investigations were reportedly completed last week, allowing their bodies to be released to their family and repatriated.