The cause of death of sisters Audrey Bélanger and Noémi Bélanger could not be formally tied to any particular substance, but a Quebec coroner has filed a report saying their deaths were probably caused by phosphine gas poisoning.

The Bélanger sisters of Pohénégamook, Que., died under mysterious circumstances in Thailand in 2012. Audrey was 20 and Noémi was 25 at the time of their deaths.

Coroner Renée Roussel revealed the details of her report on their deaths at Rivière-du-Loup High School on Monday morning.

"Science doesn't allow us to confirm this without a doubt. Maybe one day it will,” Roussel said.

Renee Roussel Quebec coroner March 2 2015

Quebec coroner Renée Roussel says she could not formally tie phosphine gas to the deaths of the Bélanger sisters, but that she believes it was responsible for their 2012 deaths. (Bruno Giguère/Radio-Canada)

She said the Quebec coroner's office redid all the work done by Thai medical examiners. She said her staff concluded that the DEET Thai examiners identified as the cause of death was not in concentrations high enough to kill the sisters.

Rather, Roussel said, it is likely that phosphine gas — a highly toxic substance — was the culprit behind the deaths, even if it was not apparent in their blood.

Roussel said about 20 Western tourists in Thailand have died in similar circumstances since 2009.

The coroner said the case of the Bélanger sisters was the most difficult investigation she has ever carried out.

Bélanger family mourns

Belanger family

Elena, Linda and Carl Bélanger said the coroner's report does little to ease the pain of Noémi and Audrey's deaths. (CBC)

Linda and Carl Bélanger, the parents of Noémi and Audrey, said the coroner's report did little to ease their pain.

Mother Linda Bélanger said the report, even if it had been conclusive, would not have helped the grieving process.

"This will follow us our whole lives," she said. "It's a wound that will never heal … Until the end of my days, I will always have this pain, this sadness."

'Until the end of my days, I will always have this pain, this sadness.' - Linda Bélanger, mother

Father Carl Bélanger said they may consider a lawsuit against the hotel or the makers of the pesticide, but that they hadn't arrived at that point yet.

Linda said they have another daughter and grandchildren to think of, and she doesn't know whether the family wants to devote its time and resources to a lawsuit.

She said it would prolong their grief and could impact the young children in their family.

"I would prefer to give this energy to my grandchildren who are growing up. I want them to have a happy life; I don't want them to see us crying all the time," Linda Bélanger said.

CBC/Radio-Canada investigation

A joint investigation by Radio-Canada's Enquête and CBC's the fifth estate concluded a highly toxic pesticide used to control bedbugs in some holiday hotels in Asia may have caused the Bélanger sisters' deaths.

Audrey and Noémi Bélanger set off on a trip through Thailand in 2012.

Days after they arrived at the popular tourist destination of Phi Phi Island, a maid found the pair dead in their hotel room.

Both were covered in vomit, and their fingernails and toenails were tinged blue.

Not the first 

The CBC/Radio-Canada investigation learned that the Bélanger sisters are not the only travellers whose deaths may be linked to this pesticide.

In May 2009, two other tourists staying on Phi Phi Island also died mysteriously.

Norwegian Julie Bergheim and American Jill St-Onge were staying in adjacent rooms at the Laleena Guest House, and they experienced similar symptoms including vomiting, dizziness and blue fingernails and toenails. Both were dead within 24 hours.

Four years after her daughter's death, Bergheim’s mother, Ina Thoresen, received a report from the Norwegian Institute of Public Health. Authorities there had consulted with leading experts from around the world about what happened to her daughter.

Although they could not state the exact cause of Bergheim’s death, they concluded that the most likely cause was poisoning from phosphine gas.