A mom and her two daughters have been found dead in their beds while her husband was discovered hanging in a stairwell.
The family dog was also found dead at their house in western France and police say none of the bodies showed any signs of violence.
Officers made the grim discovery after they were called by the woman’s mother.
She was concerned that she had not been able to make contact with her daughter, according to local media reports.
Police and firefighters found the 41-year-old man hanging on the stairwell on the ground floor at 10am on Sunday.
The bodies of the two girls, aged 8 and 11, were found in their beds on the first floor and their 38-year-old mother on the second floor, in the marital bed.
The family dog was also found dead at the house, in the town of Carantec, Brittany.
Prosecutors have said none of the bodies show “any trace of external injury or the use of a weapon”.
The mum and her two daughters show “symptoms of poisoning”, an investigating source explained.
The couple were in the process of separating at the time of the tragedy, the paper added.
Autopsies are due to be performed to determine the causes of death.
The man reportedly worked in a marble factory in the region and his wife worked as in sales.
Flowers have been placed outside the house, which is on a small hill surrounded by fields near the sea.
It comes as four members of a French family were found dead and the only survivor was seriously injured after they allegedly leapt off a balcony.
Police were called to the scene in Montreux, Switzerland, after reports that five people had jumped together from a building next to a casino.
Police reported that the dead are a man, 40, his wife, 41, their daughter, 8, and the woman’s 41-year-old twin sister.