A report into the death of a New Zealand woman in Thailand has been put down to exposure to toxins, but authorities say they cannot be more specific.
Sarah Carter, 23, died after falling ill while staying at a hotel in Chiang Mai, in northern Thailand, on 3 February this year.
Four other tourists and a local guide died in similar circumstances about the same time.
The Thai Department of Disease Control on Tuesday released a final report into the deaths.
It states that, despite the best efforts of Thai and international experts, the tourists are likely to have been exposed to some toxic chemical, pesticides or gas - but the exact cause cannot be identified.
The department says more than 350 drug, chemical and organism tests were done in each case, and 1250 relating to Ms Carter.
The Thai report says it is unlikely pesticides used against bedbugs were to blame for some of those deaths.
A UN chemicals expert specialising in pesticides Dr Ron McDowall, who tested swabs from Sarah Carter's hotel room and who believed bedbug chemicals were to blame, told Checkpoint he's been vindicated.
"I think they've got it right - it's a chemical, its likely to be pesticide, whether it's an organo-phosphate or an organo-chlorine and at the end of the day Sarah Carter's been killed by an over-enthusiastic spraying company," he says.
Meanwhile, the Thai authorities are taking measures to reduce the risk of exposure for visitors to Chiang Mai.
These include stricter measures for the use of chemicals including the use of pesticides in hotel and market areas, but Dr McDowall says he is not convinced that same thing won't occur again, despite the regulations.
Sarah's father, Richard Carter, told Checkpoint he will closely follow the report's claim that stricter measures will be taken for chemicals near hotels and markets.