Chlorpyrifos is banned in many countries and in any case should only be used under very controlled circumstances.
The programme makers found traces of it, despite extensive cleaning, three months after the deaths.
Meanwhile on the programme the Governor of Chiang Mai says he still believes the deaths were a co-incidence, and the Medical Chief of the city says he suspects a chemical, but will not say what, and will not name the owner of the hotel.
If what '60 Minutes' believes is true then of course it's nothing short of a national scandal. The whole affair has the terrible odour of a cover-up. What is further it shows how weak are the missions of Canada, the United States, and France, all of whom had nationals in Chiang Mai, in actually looking after their nationals in getting information from the Thai government.
The father of 23-yr-old Sarah Carter seems to have no doubt. There was a cover-up. Moreover Richard Carter believes that the authorities in Chiang Mai tried to hide things from '60 Minutes'. He told the New Zealand Herald:
"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."
The Downtown Inn in Chiang Mai is owned by a former Mayor. I was part and parcel of exposing the deaths in the hotel and providing the links.
Of course I knew from the beginning that the local press in Chiang Mai did not want to attend to this story with a critical eye because I was told by a local journalist there, who had been given misinformation, that he was in a 'no-go' area.
Thailand could have done itself a big favour by being open and transparent from day one. Statements that the deaths were a 'co-incidence' still being repeated are not helpful.
There is a part of me that says that I hope '60 Minutes' is wrong. But they walked into the hotel as the management continued the scrubbing of all rooms on the fifth floor.
But I have done work for both the US 60 Minutes and the Australian '60 Minutes' and a producer from NZ TV's '60 Minutes' was in touch with me last week (although there was little I could personally do to help) Programmes in the '60 Minutes' stable do tend to err on the side of caution.
I would like to see the Chiang Mai authorities come clean. My experience in Thailand suggests that doctors and professional scientists do not cover-up, but sometimes their hands are tied.
And as it transpires the programme shows that the medical people in Chiang Mai are not at fault and were helpful in making the programme. It is very difficult to find a trace of chlorpyrifos in a human more than 24 hours after that person is infected.
But an investigation should have discovered what the hotel owner was spraying in his rooms a long time ago.
It seems to late now for a bit of face-saving. This story has gone viral and I am getting request for copy and pictures from several countries.