Are you implying their deaths have nothing in common?
They ate the same food, took the same drugs.
Start the investigation there.
The chances of them spraying only the two rooms used by a pair who were travelling together?Probably pesticide for bedbugs again. Chlorpyrifos?
No, if you hear about a Thai having been smuggled out down the back stairs a day or two earlier and the death kept out of the press, as happened at the Doomtown Hotel in Chiang Mai, then that's a different story.