The father of a New Zealander who died suddenly in Thailand suspects Thai authorities have covered up the circumstances surrounding her death to protect their tourism industry.
An investigation has found traces of a potentially lethal toxin in the Thai hotel where 23-year-old Wellington woman Sarah Carter became fatally ill.
Ms Carter died and her friends Emma Langlands and Amanda Eliason became gravely ill while on holiday in Chiang Mai, Thailand.
Traces of chlorpyrifos, which is used to kill bedbugs but has been banned in other countries, have been found in samples that current affairs television show 60 Minutes had independently tested.
United Nations scientist Ron McDowall said there was a strong likelihood Ms Carter died from excessive exposure to the substance, which causes identical symptoms to those suffered by the trio as well as several other tourists who died after staying at the hotel.
The fact traces of chlorpyrifos were found three months after Ms Carter's death and after the room was cleaned suggested there was a high concentration when she was staying there.
"I think she has been killed by an overzealous sprayer who's been acting on the instructions of the hotel owner to deal with bed bugs," Mr McDowall said.
Even a slight mistake in the dosage of chlorpyrifos, which has been banned for indoor use in many countries, could be lethal, he said.
Ms Carter's father, Richard, said on the face of it, the evidence presented by the investigation was strong.
"Whether it would stand up in court may well need to be put to the test, but I believe it was done very professionally and thoroughly ..."
The investigation showed teams of Thai workers intensely cleaning rooms on the fifth floor of hotel, where Ms Carter and her friends became ill.
Mr Carter believed this was an attempt by the Thai authorities to get rid of evidence pertaining to her death in order to minimise damage to the country's lucrative tourism industry.
"I think they've proven that they really don't have an interest in resolving the issue, calling it a co-incidence for a start, and also to have systematically gone around and covered up as much of the evidence as they possibly could when they had wind that TV3 were about to do an investigation.
"There have been quite a number of incidents where the reaction from the Thai authorities is to cover things up to save their own tourism industry, without taking the long-term view of resolving these problems and making the country safer for all visitors, as well as their own people."
Mr Carter, who has started a website dedicated to sharing stories of travellers struck by tragedy in Thailand, said he would continue pushing for answers about his daughter's death until those responsible were brought to justice.
"I feel if no one's made accountable then they're just going to carry on down the same track, operating like cowboys with no health and safety standards."
Mr Carter said he had been assured by a senior Thai health department official there would be further investigation.
Mr McDowall checked his theory with other experts from New Zealand and Italy, who supported his belief that Carter was killed by the chemical.
"Their reaction was that it's quite clear that it's chlorpyrifos poisoning... the symptoms are the same, the pathology is the same and the proxy indicates that the chemical was present in the room."
A Thailand police inspector said police were looking into the possibility the tourists were killed by over exposure to pest control chemicals.
However, Mr Carter said it was "good to get an answer" about how his daughter died.
"It's still pretty horrific that they have such low standards that that can happen," he said.
"The Thais are very good at sending off Western drug traffickers to the gallows, so this will be the test of how serious they are when it comes to looking at criminal negligence involving their own people and will really show the world whether there's one standard for everyone or whether there are two different standards - one for Westerners and one for their own people."
Sarah Carter's mother, Anna Carter, said she hoped action would be taken so other tourists would not die.
- The Dominion Post and NZPA