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.
Sarah Carter, 23, fell violently ill on February 3 while staying at the Downtown Inn in Chiang Mai and died a day later.
Her two kiwi friends and travelling companions, Emma Langlands and Amanda Eliason, also fell ill but later recovered.
An investigation aired by TV3's 60 Minutes last night showed trace elements of the chemical chlorpyrifos, used to kill bed bugs, were found in the hotel room Ms Carter was staying in.
United Nations scientist Ron McDowall, who carried out tests on behalf of TV3, said the symptoms suffered by Ms Carter and the other tourists who died suggested they were killed by over exposure to the chemical.
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," Dr McDowall said.
Dr McDowall checked his theory with other experts from New Zealand and Italy, who supported his belief that Ms Carter was killed by the chemical.
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 by TV3."
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 coincidence 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 that there would be further investigation.
The way Thai authorities dealt with the incident would have serious implications for the way the Thai judicial system was perceived by the West, 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."