The suppression of vital information about the deaths of Noemi and Audrey Belanger comes despite a call by the sisters' father for details of the deaths to be made public.
Today Ryan Kells, the fiance of American Jill St Onge who died in equally mysterious circumstances with Norwegian Julie Bergheim on Phi Phi in 2009, echoed the call for information to be made public.
''I would love to have a more detailed investigation,'' he told Phuketwan. Three years ago, Mr Kells was quickly bundled off Phi Phi with the body of Ms St Onge in the bottom of a speedboat after the first pair of mysterious deaths.
Now the toll of young women killed without cause on Phi Phi has risen to four and information remains scarce.
An article posted on Phuketwan on Friday revealed for the first time that an autopsy on the Belanger sisters showed the presence of insecticide, according to local police.
Canadian news reports established the chemical as DEET, according to a journalist who has viewed the results of an autopsy. Other reports have since suggested the poison may have been drunk by the sisters in a euphoria-inducing cocktail known locally as 4x100.
The concoction, usually drunk by young partiers on Phi Phi from plastic buckets of varying sizes, contains cough syrup, cola, ground-up leaves of kratom - a natural drug - and ice.
Today police were quoted in the Thai media as saying results from the autopsy in Thailand have been sent to Canadian embassy officials.
Despite the call by Carl Belanger for more information, Canadian government officials are, like the Thai authorities, reluctant to reveal more about the deaths of Audrey, 20, and Noemi, 26, almost three month ago.
The lack of information plays into the hands of tourism-related businesses in Thailand that are not entirely legal and prefer to cover up mysterious deaths rather than have the spotlight shone on their practices.
Law enforcement officers are seldom evident after legal drinking hours on holiday islands in Krabi, the province where Phi Phi retains a strong attraction for 20-somethings who want to take in the sights by day and alcohol with additives in ''buckets'' by night.
Although there is no direct evidence that the Belanger sisters died from a drink laced with deadly DEET, there are few other ways that the chemical could have entered their bodies in a quantity potent enough to kill.
In contrast to the police, Edthirit Kingleg, President of the Tourist Association of Krabi, called for greater disclosure of the details of the autopsy and the investigation.
''Everywhere young tourists go there are drugs,'' he said. ''I don't want to have the image of Krabi damaged.''
He said the local tourist industry often went on ''road shows'' to overseas markets to sell the natural beauty of Krabi to tourists.
''When they come and they have an issue like this, it's very bad for Krabi tourism.''
He said the it was well-known that businesses operated beyond the law in catering to the young tourists who came to Phi Phi and Krabi to enjoy the nightlife as well as the snorkelling and diving.
''The Krabi provincial authorities should do their job and control the entertainment areas on Phi Phi, Koh Lanta and Ao Nang,'' he said.
''All businesses catering to young travellers must be checked. If the authorities do not act, in the long term it will damage the good image of Krabi.''
Mr Edthirit said he was shocked because this was the second time that two young women had died on Phi Phi and the authorities had yet to determine a cause.
''We hear about this issue in Thailand from the international media, not from the people who should be telling us, the local authorities,'' he said.
After the mysterious deaths of several tourists in the northern Thai city of Chinag Mai last year, Thai authorities undertook to fully investigate tourist deaths in future and provide speedy updates on the causes.
That promise appears to have been quickly forgotten.
Local businesses are still scrambling to prevent the deaths of the Belangers damaging their visitor numbers, just as they did when pushing Ryan Kells off Phi Phi with the body of Jill St Onge, 27, in the bottom of the boat in 2009.
Results of a second autopsy on the sisters, undertaken in Canada, have also yet to be revealed.
With Mr Belanger calling for more information to be made public, the Canadian authorities' commitment to ''privacy'' and their reluctance to make any details public is likely to be questioned.
In 2009, Mr Kells and Ms St Onge's family were highly critical of the sketchy and inconclusive nature of the autopsy conducted on her in Thailand.
The body of Ms Bergheim, 22, was returned to Norway where a second autopsy also failed to determine a cause for her death.
Mr Kells and Ms St Onge were staying in a room at Laleena Guesthouse on Phi Phi, with Ms Bergheim and another Norwegian in a next-door room.
All four tourists fell sick within hours of each other at Laleena. Mr Kells and Ms Berheim's friend, Karina Refseth, 21, narrowly escaped the same fate as their companions.