The Superintendent of Krabi Town polce, Colonel Jamroon Rumrom, said police were now awaiting the results of the autopsy performed on the sisters in Bangkok earlier this week.
''We checked out the prospect of any kind of violence involved in their deaths and have ruled that out,'' he said.
''There is no need to highlight the presence of a couple of men on the security footage because they had no connection to the deaths of the women.''
The bodies of the two girls - Noemi, 26 and Audrey, 20 - were due to arrive back in Canada yesterday after being autopsied at the Forensics Department of Bangkok's Ramathibodi Hospital on Tuesday.
It is likely that second autopsies will be conducted in Canada, although officials at the Canadian Embassy have so far maintained silence about the mysterious deaths and their involvement in trying to establish a cause.
Police are now waiting for the report from the autopsies, which should be available on Tuesday week. Colonel Jamroon said today that food poisoning or some other kind of poisoning was the likely cause of death.
''We are really not in a position to speculate,'' he said. ''But I have had one call from a Thai woman, married to a French-Canadian from the Quebec region, where the dead women are from.
''She said her husband suffered a very strong allergic reaction when he ate seafood in Thailand for the first time.''
A nurse at Phi Phi hospital told Phuketwan yesterday that there were cases of food poisoning on the popular holiday island every day. ''Some visitors don't want to stay here - we only have a doctor and five nurses - and are too sick to stay on Phi Phi,'' she said.
''The number of food poisoning cases is not unusual. We are able to treat most of them here.''
Dr Jiraphan Teaphan, Director of Krabi's Public Health Office, said seafood on Phi Phi was usually much fresher than seafood in other parts of the province.
''The quality of food of all kinds is usually very good on Phi Phi,'' he said. ''Chemical sprays are used on vegetables so there cannot be a 100 percent guarantee of purity.''
He said it was unlikely that the girls had fallen victim to puffer fish. ''Nobody catches them and serves them,'' he said.
''There would be no need to serve puffer fish when there are so many good eating fish caught off Phi Phi.''
Turtle meat killed a couple of sea gypsies on Phuket last year after they poached the creatures and unusual crabs have also caused poisoning.
''It's better to wait to see what the results of the autopsy tell us,'' he said. ''There is no point at this stage in jumping to any conclcusions.''
The girls' bodies were found in their resort room on Phi Phi a week ago. Mystery has since surrounded the cause of their deaths.
In 2009, American Jill St Onge, 27, and Norwegian Julie Bergheim, 22, were staying in adjoining rooms at Laleena guesthouse on Phi Phi when they both fell ill and died within hours.
Ryan Kells, Miss St Onge's finance, later told of being rapidly ''pushed off'' Phi Phi in a speedboat with the body of his girlfriend in the bottom of the boat.
While Ms St Onge was cremated, the body of Julie Bergheim was returned to Norway where leading pathologists conducted a second autopsy.
Like the first autopsy conducted in Thailand, no cause of death could be determined.
Last year, the mysterious deaths of New Zealander Sarah Carter, 23, and four others left a similar mystery in the northern Thailand holiday city of Chiang Mai, with no formal cause of death established.
A receptionist at a Phi Phi resort said the latest mysterious deaths were likely to affect tourism but people on Phi Phi were hoping the island would continue to attract substantial numbers of 20-something travellers.
''Once trhe results of the autopsies are released I am sure people will carry on and not be concerned.''
He said authorities who are supposed to check health and safety matters on Phi Phi usually came from the mainland and treated the trip to Phi Phi as ''a bit of a holiday.''
''Standards are not enforced on Phi Phi as rigidly as they should be,'' said the receptionist, Chatchaiwan Keddee.