Yes, Vikane could be a culprit. Note that by itself it has no odor or color and you need to add another chemical to it to make sure people can smell it (and be warned). I can see the Thais skipping this step.
I’d like to know if it is available in Thailand.
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Only a small margin exists between lethal and non-lethal exposures”.
See url for more details.
PHYSICIAN'S GUIDE TO PESTICIDE POISONING