In an attempt to rid their rooms of bed bugs, a Thai hotel may have inadvertently killed seven of its guests.

An investigation by New Zealand's 60 Minutes discovered high levels of the pesticide chlorpyrifos, a chemical banned for indoor use in many countries but used in the hotel room where Kiwi backpacker Sarah Carter died in February.  The samples were gathered as reporters pretended to be guests and entered the fifth floor where Carter stayed.

United Nations chemical expert Dr. Ron McDowall told the Daily Mail, I think (Carter ) has been killed by an overzealous sprayer who has been acting on the instructions of the hotel owner to deal with the bed bugs.  However, proving this will be tricky.  It is near impossible to confirm poisoning from blood samples because chlorpyrifos is quickly absorbed by the body and has a half-life of just one day. 

All seven victims stayed at or used facilities at the Downtown Inn in Chiang Mai, a popular backpacker destination in northern Thailand.  A retired British couple that arrived the day Carter died was found dead in their room several days later.  Canadian Bill Mah was discovered dead in the Inn as well.  His death was attributed to suspected natural causes.  A young Frenchwoman, an American tour guide, and a Thai visitor passed away between January and March bringing the total to seven guests of the Downtown Inn with suspicious deaths.

Police initially dismissed the mysterious events as food poisoning cause by toxic seaweed from a nearby food stall.  Thai authorities had continually stated that the deaths linked to the three-star hotel were coincidental.   However, after a recent raid of the insect eradication company, Chiang Mai's head of public health stated, It's possible that they mixed together the wrong chemicals.

Two years ago, American Jill St Onge and Norwegian Julie Bergheim died under similar conditions at a different Thai resort.  There are fears that some Thai hotels may be using unsafe chemicals.

With rooms starting at $41 a night, the Downtown Inn remains open.